Automotive circuit diagram knowledge

Two, three circuit diagrams

1.Wiring diagram

The wiring diagram is based on the general position of the automobile electrical appliances on the car body, as shown in Figure 8-6.

Its characteristics are: the number of electrical appliances (ie electrical equipment) in the entire vehicle is obvious and accurate, the direction of the wires is clear, there is a beginning and an end, it is easy to track the line, and it is more convenient to find.It pressWire harnessCompile and assign the wires to each wire harness to strictly match the position of each plug-in unit. In the vicinity of each switch, a table shows the connection and gear control relationship of the switch, the connection relationship between the fuse and the wire, and the color and cross-sectional area of ​​the wire.

Disadvantages of wiring diagrams: the wires on the diagram are crisscrossed, the printed layout is small, it is difficult to distinguish, the layout is too large, and the printing is restricted; reading and drawing are time-consuming and laborious, and it is not easy to grasp the key and difficult points of the circuit; it is not easy to express the internal structure and working principle of the circuit .

2.Schematic diagram

◇ Schematic diagram of the whole vehicle circuit:

For the needs of production and teaching, it is often necessary to find the beginning and end of a certain circuit as soon as possible in order to determine the route of failure analysis. When analysing the cause of the failure, it should not be limited to a certain part in isolation, but the position of this part of the circuit in the entire vehicle circuit and the connection with the relevant circuit should be expressed. The advantages of the whole vehicle circuit diagram are:

(1) There is a complete concept of the whole car circuit, which is not only a complete whole car circuit diagram, but also a partial circuit diagram interconnected with each other. The key and difficult points are prominent, and the complexity is appropriate.
(2) The concept of high and low potential is established on this diagram: its negative pole “-” is grounded (commonly known as grounding), and the potential is the lowest, which can be represented by the bottom line in the figure; the positive pole “+” has the highest potential, and the most The upper line indicates. The direction of the current is basically from top to bottom, the path is: power supply positive "+" → switch → electrical appliances → ground → power supply negative "-".
(3) It is possible to reduce the twists and turns of the wires, the layout is reasonable, the drawing is simple and clear, and the graphic symbols take into account the appearance and internal structure of the components, which are convenient for readers to associate, analyze, and are easy to read and draw.
(4) The local circuits (or subsystems) are connected in parallel with each other and the relationship is clear. The connection points between the generator and the battery and between the subsystems should be kept in place as much as possible. The connections of fuses, switches and meters are basically the same as The original picture is consistent.

◇ Schematic diagram of partial circuit:

In order to understand the internal structure of automotive electrical appliances, the relationship between the various components, and understand the working principle of a certain partial circuit, it is necessary to extract a certain partial circuit that needs to be studied from the circuit diagram of the whole car, and refer to other detailed information. According to field surveying and mapping, inspection and test records, the key parts are enlarged, drawn and explained. This kind of circuit diagram uses less electrical appliances and small format, looks simple and clear, easy to read and draw; its disadvantage is that only part of the circuit can be understood. Figure 8-7 shows the schematic circuit diagram of the Poussin engine.

3.Harness diagram

The wiring harness diagram of the whole vehicle circuit is often used for the connection, maintenance and wiring of the assembly line of the automobile factory and the repair shop. The wiring harness diagram mainly shows the connection parts of the electrical appliances in the wiring harness, the markings of the terminals, the wire ends,Connector(Connector) Shape and position, etc., it is the car circuit diagram that people can actually touch in the car. This kind of diagram generally does not describe the wire direction inside the wire harness in detail, only the wire heads and connectors exposed outside the wire harness are numbered or marked with letters in detail. It is a circuit manifestation that highlights assembly marks, which is very convenient for installation, wiring, inspection and maintenance. If the line ends of this figure are marked with serial numbers and colors accurately and used in combination with circuit schematics and wiring diagrams, it will play a greater role and receive better results. Figure 8-8 is the front wiring harness diagram of Beijing BJ2020 light off-road vehicle.

Third, the wiring law of general automotive circuits

The car circuit generally adopts a single-wire system, electric equipment is connected in parallel, the negative electrode is grounded, the circuit is distinguished by color and number, and the whole car circuit is divided into several main lines with the ignition switch as the center, namely: battery live wire (line 30), Accessory live wire (Acc line), key switch live wire (line 15).

(1) Battery live wire (line B or line 30)

Lead through the fuse box from the positive electrode of the battery, and also connect the live wire of the car battery to the starter live wire terminal, and then lead a thinner live wire from there.

(2) Ignition indicator light line (IG line or line 15)

Ignition switch is in ON (working) and ST (starting) gears to have electricity, there must beCar keyTo be connectedIgnition system, Pre-magnetization, instrument system, indicator light, signal system, important circuit of electronic control system.

(3) Dedicated line (Acc line or 15A line)

Used for electrical appliances that need to be connected when the engine is not working, such as retractors, cigarette lighters, etc. The ignition switch is set to a single gear for power supply, but the radio and the like still need to work at the same time as the ignition instrument indicator when the engine is running, so the contact structure of the ignition switch knife and the contact needs to be specially designed.

(4) Start control line (ST line or No. 50 line)

The control switch (contact plate) of the main circuit of the starter is usually turned on and off by a magnetic switch. The attracting coil and holding coil of the magnetic switch can be controlled by the starting gear of the ignition switch. The attracting and holding coil current of the high-power starter is also very large (up to 40~80A), and it is easy to ablate the "30-50" contact pair of the ignition switch. A starter relay must be installed separately (such as Dongfeng, Jiefang and Mitsubishi Heavy vehicle). For cars equipped with automatic transmissions, in order to ensure neutral start, a neutral switch is often placed in series on the 50th line.

(5) Grounding wire (grounding wire or line 31)

In the car circuit, the wiring method that uses the component and the metal part of the body (frame) as a common wire is called single-wire system, and the part where the body and the electrical appliance are connected is called grounding or grounding.
The grounding points are distributed all over the car. Due to the connection of different metals (such as iron, copper and aluminum, lead and iron), the electrode potential difference is formed. Thin sheet metal parts may cause poor grounding, such as the light does not turn on, the meter does not work, and the horn does not sound. It is necessary to pay equal attention to the grounding part and the live wire connection. Therefore, Hyundai Motor adopts a two-wire system in some parts, with special public grounding contacts, and special grounding circuit diagrams, which can be parallel with the fuse circuit outline diagram. In order to reduce the line contact voltage drop when starting, the battery pole pile chuck, the frame and the engine body are all connected with a large cross-sectional area of ​​the ground wire, and the contact parts are thoroughly derusted, painted, and tightened.

Fourth, the general points of reading circuit diagrams

(1) Looking at the "whole car", focusing on the "partial"-from "centralized" to "distributed".
The whole vehicle circuit is generally composed of various partial circuits, which express the connection and control relationship between the various partial circuits. To separate the partial circuits from the general drawing of the whole car, it is necessary to master the basic conditions and wiring rules of each unit circuit.
The basic characteristics of the car circuit are: single-wire system, negative pole grounding, and electrical appliances in parallel with each other. Each unit (partial) circuit, such as power supply system, starting system, ignition system, lighting system, signal system, instrument system, etc., has some of its own characteristics. The circuit should be guided by its own characteristics to decompose and study the whole Car circuit, this will reduce blindness, and can read car circuit diagrams more quickly and accurately.
At the beginning, you must read the legend several times carefully, check the approximate location and quantity of the electrical appliances on the car against the wiring diagram, the purpose of the electrical appliances, and whether there are novel and unique electrical appliances. If so, you should pay extra attention.

(2) Grasp the function of the "switch"-the "object" under control. The switch is the key to control the on-off of the circuit. Pay special attention to the relay not only the control switch but also the controlled object.

(3) Look for the "loop" of the current-the "path" of the controlled object.
The circuit is the simplest electrical concept. Regardless of the electrical appliances, if they want to work normally (convert electrical energy into other forms of energy), they must form a path with the positive and negative poles of the power source (generator or storage battery). That is: starting from the positive pole of the power source → passing through the electrical appliances → returning to the negative pole of the same power source. This simple and important principle must be used no matter what circuit diagram is read, but it is often neglected when reading car circuits and can't figure it out.

Five, reading examples

Figure 8-9 shows the circuit diagram of the Santana 2000 GSi car engine electronically controlled gasoline injection and ignition system provided by the manufacturer. This diagram is a circuit wiring diagram that is relatively close to the circuit schematic.
Fundamentally speaking, to understand automobile circuit diagrams, you must first have a certain basic knowledge of electrical engineering and electronics, familiar with the structural principles of automobile electrical ,TerminalConnection with wires, contacts and switches, electrical components, meters,sensor, Electrical equipment, and some limited symbols) and the general structural characteristics of automotive electrical circuits. On this basis, start with the more familiar models, from simple to complex, organize and summarize, gradually in-depth, and even comprehend by analogy.
As the current circuit diagrams of various types of cars are not standardized, especially the graphic symbols of various imported cars are still very inconsistent, many maintenance personnel are not familiar with the structural principles of electronically controlled cars, so they must understand the circuit diagrams of various models. Certainly difficult. Now combine the circuit of the electronically controlled gasoline injection and ignition system of the Santana 2000 GSi car engine (Figure 8-9) to summarize several key reading methods.

(1) Master the characteristics of specific circuit diagrams

Take the circuit diagram of the Santana car as an example. Compared with the circuit diagrams of other models, this circuit diagram has certain characteristics. It is not only used to express the line direction of the main components in the automotive electrical system, but also expresses the structure of the electrical circuit. Its main features are as follows:

1.The basic circuits are arranged in order of the system

From the figure, the entire circuit is arranged vertically, the circuits of the same system are summarized together, and the space occupied in the circuit diagram is limited to a certain range (as shown in Figure 8-9 for the circuit of the engine gasoline injection and ignition system) part).

2.The whole circuit rarely turns and crosses

For some electrical appliances with more complicated lines, in order to make them organically connected without destroying the verticality of the drawing, the method of broken wires with numbers is used to solve them. For example, corresponding to the circuit number "8" at the bottom of the circuit diagram, a small box is drawn at the end of the upper half of the circuit, and the internal mark is "23", indicating that the lower half of the circuit should be found at the position of the circuit number "23" ; Similarly, there is also a box at the beginning of the lower half of the circuit at the "23" position, with an internal mark of "8", indicating that the upper half of the circuit should be searched for at the circuit number "8". Through these 4 numbers, the upper and lower sections of the same circuit drawn in different positions are connected.

3.The entire circuit protrudes centered on the central junction box

The part above the 5th horizontal line above the circuit diagram shows the devices and wires installed in the central junction box. For example, in Figure 8-9, J17 is the fuel pump relay, and the number in the small box on the upper side is 2, which means that the relay is plugged into the No. 2 position on the front panel of the central junction box. The fuel pump relay J17 is marked with 4 groups of numbers 2/30, 4/86, 3/87, 6/85, among which the denominator 30, 86, 87, 85 refers to the label of the 4 pins on the relay, and the numerator is 2 , 4, 6, 3 refer to the corresponding 4 jacks on the No. 2 position on the front panel of the central junction box. For another example, S5 is a fuel pump fuse, located at the fifth position from the right of the fuse installation part under the front panel of the central junction box, with a rated current of 10A. The 5th horizontal line above the circuit diagram is marked with the codes D, N, P, E, etc. of the connector on the back of the central junction box. The number after the code indicates the position of the socket of the wire connected to the connector in the connector For example, E14 represents the 14# jack on the connector E, and N represents the connector has only one jack; in the same way, D23, D7, and D13 represent the 23#, 7#, 13 of the connector D, respectively # Jack, and all the wires whose contacts are marked with the same code are in the same wiring harness on the car, which also provides convenience for finding circuits in actual work.

4.The molded copper sheet in the central junction box is represented by 4 horizontal lines above the circuit diagram

The 4 horizontal lines at the top of the circuit diagram are used to represent the molded copper sheets press-fitted in the plastic body of the central junction box. Three of them are live wires for different purposes introduced into the junction box, and one is a ground wire. The line end marked "30" is the live wire directly connected to the positive electrode of the battery; the line marked "15" is the power supply line of the small-capacity electrical appliance controlled by the ignition switch from the ignition switch 15 terminal; the mark is "X "Is the power supply line of large-capacity electrical appliances controlled by the load-reducing relay. Only when the contact of the load-reducing relay is closed, can the current of line 30# be introduced into line X#; Connect with the ground point of the central junction box bracket.

5.The circuit diagram shows the grounding method and location of the electrical appliance

The horizontal line at the bottom of the circuit diagram represents the ground wire, and the ground terminal of the wire is marked with a circled number code. The grounding position of each code is shown in the legends of Figure 8-9. It can be seen that in the car, not all electrical appliances are directly connected to the metal car body for grounding, some are connected through grounded sockets, and some are grounded through other electrical appliances or electronic equipment.

6.Unified representation of the connecting plugs in the line

The connecting plugs in the circuit are uniformly coded with the letter T, and the following numbers indicate the number of holes of the plug and the serial number of the holes corresponding to the connecting wires. For example, T4/2 indicates that the plug has 4 holes, and the corresponding jack number of the connecting wire is 2; T80/71 indicates that the plug (T80 is the connecting plug on the electronic control unit) has 80 holes, and the corresponding jack number of the connecting wire is 71. The connecting wires in the circuit are marked with the diameter of the copper core cross-sectional area (mm), and some circuit diagrams also use Chinese characters or English letters to indicate the color of the wire.

After clarifying the above-mentioned characteristics of the circuit diagram of the Santana car, and then according to the general circuit diagram reading essentials, it is not difficult to understand this circuit diagram.

(2) The essentials of reading general circuit diagrams

1.Compare the legends and graphical symbols, and be familiar with the names of related components and their positions, quantities and wiring in the diagram
For example, in Figure 8-9, G6 is the fuel pump, J17 is the fuel pump relay, S5 is the fuel pump fuse (10A) and so on. One end of the fuel pump is connected to the output end of the fuel pump relay J17 through the fuse S5, and the other end is connected to ③—the star grounding socket on the left side of the central junction box.

2.Analyze the circuit according to the "loop principle"

Any circuit should be a complete electrical circuit, including power supply, switch (or fuse), electrical appliance (or electronic circuit), wire and connector, etc., and from the positive pole of the power supply through the wire, switch (or fuse) to Ground the iron after using the electrical appliances and return to the negative pole of the same power source. Still take the fuel pump as an example: the power supply goes from the positive electrode of the battery (30# power cord) through the closed fuel pump relay contact, fuse S5 to the fuel pump (motor) C6, and then through the star grounding socket on the left side of the central junction box ③ Ground the iron and return to the negative terminal of the battery.

3.Pay attention to the state of the switch or relay in the circuit

Most electrical appliances or electronic devices form a loop or change the loop to achieve different functions through different states of switches (including electronic switches) or relays. For example, the above-mentioned fuel pump circuit can only be formed when the fuel pump relay contacts are closed, and the condition for the fuel pump relay contacts to be closed is that the relay coil is electrically connected. In the same way, it can be seen from the circuit diagram that the fuel pump relay coil must form a loop through the grounding point in the electronic control unit when the transistor that functions as a switch in the electronic control unit J220 is turned on. For circuits that use multi-stage ignition switches or combination switches, you should also pay attention to how the battery (or generator) current reaches the switch, whether it passes through other switches or fuses in the middle, and which terminal of the switch is the live wire connected to; The multi-shift switch has several gear positions. There are several simultaneous or separate action knives inside the switch. Which appliances are turned on or off in each gear position; which switches or buttons are combined by the combination switch, and which ones pass through The contacts make the circuit or change the circuit, etc.

4.We must be good at using the characteristics of car circuits and break the whole car circuit into parts

The single-wire system of the automobile circuit, the parallel connection of each circuit load, and the parallel connection of the two power supplies provide convenience for dividing the entire vehicle circuit into parts for reading the picture. The circuit of the whole vehicle can be analyzed one by one according to the various sub-circuits that make up the electrical circuit of the automobile as described above; for each sub-circuit, the methods of breaking down can also be adopted to read. For example, the electronic control system circuit can be divided into the engine electronic control system, the automatic transmission electronic control system, the brake anti-lock electronic control system and other circuits; the engine electronic control system can be divided into gasoline injection control, ignition control, emission control, etc. Circuit.