one. characteristics and general rules of car wiring
Generally, a single-wire system, parallel connection of electrical equipment, grounding of the negative electrode, and lines with different colors and numbers are used to distinguish the lines, and are divided into several main lines with the ignition switch as the center.
1. Battery positive wire: lead through the fuse box from the battery, and some lead directly from the battery positive wire to the positive terminal of the starter, and then lead the thinner positive wire to other circuits.
2. Ignition, instrument, indicator line: the circuit can only be connected through the car key.
3. Dedicated line: electrical appliances that need to be connected regardless of engine operation, such as a retractor and a cigarette lighter, are powered by a separate ignition switch.
4. Start control line: The control switch (contact plate) of the main circuit of the starter is usually turned on and off by a magnetic switch. There are three forms of wiring: the attraction coil holding coil of the magnetic switch of the low-power starter is controlled by the ignition switch’s starting gear; the attraction holding coil of the high-power starter is controlled by the starter relay (such as Dongfeng Jiefang and Mitsubishi heavy vehicles); -For cars equipped with automatic transmissions, in order to ensure neutral start, the start control line is often connected to the neutral switch in series.
5. Grounding wire: the grounding points are distributed throughout the car and connect with different metals (such as iron, copper and aluminum, aluminum and iron) to form electrode potential differences. Some grounding parts are easy to be contaminated with muddy water, oil, or rust, and some are connected. The iron part is very thin sheet metal, which may cause poor grounding, such as the light does not work, the instrument does not work, and the horn does not sound. Therefore, some cars use double wire.
two. Second, the power system wiring law
1. The generator is connected in parallel with the battery, and the negative electrode of the battery must be grounded. The positive electrode of the battery is connected to the positive electrode of the motor via an ammeter (or directly). The static electromotive force of the battery is usually 11.5V～13.5V, and the output voltage of the generator is usually limited to 13.8V～15V (24V electric system 28V～30V). The normal voltage of the generator is 0.3～3.5V higher than the voltage of the battery when it is working. This is mainly to overcome the line voltage drop, so that the battery can be fully charged and not overcharged.
2. The terminals of the domestic silicon rectifier generators are marked or named, “ten” or “Bten” is the “armature” terminal, this terminal should be connected to the ammeter or the “ten” pole of the battery; “F” It is the “magnetic field” terminal, which is connected to the regulator’s “magnetic field” terminal; “E” is the “ground” terminal, which should be connected to the regulator’s “ground” terminal.
3. There are two ways to ground the magnetic field coil of the AC generator with external regulator: one is that the magnetic field coil is grounded directly inside the generator, such as the generator of the domestic Dongfeng EQ1092 BJ2020 automobile; the other is that the magnetic field coil does not The generator is grounded internally, but through the regulator, such as the alternator of the Jiefang CA1092 car.
Three, start the system wiring law
1. The ignition switch directly controls the circuit of the starter: the ignition switch directly controls the suction and pull holding coil of the starter in the start gear, which is mostly used in the car circuit of the starter below 1.2KW; the current of the magnetic switch coil of the starter above 1.5KW is Above 40A, use the start relay contact as a switch.
2. Starter control circuit with starting protection: When the starting ignition switch is at gear 0, the circuits are all disconnected. When the ignition switch is in gear 1 (not started), the power supply circuit is provided by: generator excitation, ignition coil, instrument, and indicator light. When the ignition switch is in the 2nd gear, in addition to the above circuit, the starter relay circuit must be connected: battery positive-ammeter-ignition switch-starter relay coil-relay normally closed contact-ground- The negative pole of the battery-the starter drives the host.
At the same time, the contact bridge connects the bypass contact of the ignition coil, the current passes through the primary of the ignition coil, and the additional resistance is isolated. After the engine is ignited, the ground voltage of the neutral point N of the generator (approximately 0.5 of the regulated voltage of the generator) disconnects the normally closed contact of the start protection relay in the start relay, cuts off the grounding point of the charging indicator light, and charging instructions The light is off, indicating that the generator is working normally.
At the same time, the grounding circuit of the starter relay coil is cut off. When the generator is working normally, even if the ignition switch is turned to the 2nd gear by mistake, the starter will not mesh with the flywheel to avoid damage to the flywheel ring gear and the starter. Protect the role of the starter.
Four, the wiring law of the ignition system
Automobile ignition system can be divided into ordinary (contact) ignition system, non-contact ignition system, microcomputer controlled ignition system and other forms. The working process is basically in the following order: primary current is turned on-primary current is turned off ( At this time, the piston of a certain cylinder is at an angle before compression top dead center)-the primary coil generates self-induced electromotive force (about 300V)-the secondary coil mutual inductance generates pulsed high voltage (about 6000 ~ 30000V)-spark plug appears .
Lead-out wires that the ignition module of the non-contact ignition system must have: 2 power input wires (4, 5 pins) controlled by the ignition switch, and the signal input wire from the signal generator (the signal generator and the distributor shaft are integrated) 3 lines (5, 5, and 3 pins, of which 5 pins are for the power supply line of the signal generator), and 2 primary current input and output lines (1, 2 pins).
Five, the wiring law of the lighting system
Automotive lighting systems generally consist of headlights, width indicators (position lights), taillights (rear indicator lights), license plate lights, instrument lights, indoor lights, etc. The headlights are divided into high beams and low beams. , Controlled with a dimmer switch. The lighting is controlled by the light switch: the light switch is turned off at level 0, the small light is not turned on at level 1 (including indicator lights, tail lights, instrument lights, and license plate lights), and the headlights at level 2 are turned on at the same time.
The current of the lighting system generally comes from the positive electrode of the battery and is not controlled by the ignition switch (because the high beam power of the headlamp is large, the light relay is usually used to control the on and off, and the second gear of the switch is used to control the relay coil). The overtaking light signal is usually indicated by the high beam light being on or off. The light switch is not used when this signal is sent, and it belongs to the short-time on button type. The lighting system of modern cars is usually controlled by a combination switch. The combination switch is mostly installed on the steering column and located on the lower side of the steering wheel. When operating, the driver can ignore the steering wheel.
Six, the wiring law of the instrument alarm system
1. All electrical instruments are controlled by the ignition switch.
2. The meter head of each meter is connected in series with its sensor, and the fuel meter and water temperature meter are generally connected with meter regulator.
3. The ammeter is connected in series between the positive pole of the generator and the positive pole of the battery. The generator charging current flows in from the positive terminal of the ammeter, and the pointer is biased toward the positive end, and when the battery is discharged, the pointer is biased toward the negative end. The following two currents do not pass through the ammeter: load current exceeding the ammeter range, such as starter, glow plug, and horn lamp current: the current supplied to other loads when the generator is working normally.
Note: When the generator is not working, the current supplied by the battery to other loads must pass through the ammeter. Modern cars often use charging instead of ammeters. The disadvantage is that the charging and discharging current is not known, and overcharging is not easy to find.
4. The voltmeter is connected after the ignition switch, and only displays the system voltage when the ignition switch is turned on. 12V systems often use 10V~18V, 24V systems often use 20~36V voltmeters.
5. Indicator lights and warning lights are often assembled with the instrument in an assembly or arranged nearby. Together with the instrument, they are controlled by the working gear (ON) and starting gear (ST) of the ignition switch. It should be possible to check whether most of the meters, indicator lights, and warning lights are in good condition in the ON position. The indicator light and the warning light can be divided into two types according to the circuit connection: one is that the bulb is connected to the ignition switch live wire, and the sensor switch is connected externally: when the switch is turned on, it forms a path with the ground, and the light is on.
Such as: charging indicator light, hand brake indicator light, brake fluid level warning light, door open warning light, oil pressure warning light, low water level warning light, etc. Another connection is to indicate that the bulb is grounded, and the control signal comes from the live terminal of other switches. Such as: high beam indicator light, turn indicator light, seat belt not fastened indicator light, anti-lock brake indicator light (ABS), cruise control indicator light, etc.
6. The bimetallic heating wire structure is commonly used in automobile instruments, and the meter head generally has only 2 wires. For example, the two terminals of the fuel indicator are arranged up and down. In general, the upper terminal should be connected to the power cord, and the lower terminal should be connected to the sensor, otherwise it will not work normally. In addition, there is a double coil cross. *. The instrument with a magnetic pointer in the middle is led out by 3 wires, one of which is connected to the ignition switch, the other wire is grounded, and the other wire is connected to the sensor.
Mechanical instruments are not connected to the circuit, such as the speedometer with flexible shaft transmission, the direct-acting elbow spring brake air pressure gauge, the oil pressure gauge, the ether expansion water temperature gauge, the oil temperature gauge, etc. These gauges have relatively high reading accuracy. It is high, but many pipelines and flexible shafts are introduced into the instrument panel, which is troublesome to disassemble and assemble, and even easy to leak. It is gradually being replaced by electronic control instruments.
Seven, the wiring law of the signal system
The signal system mainly includes oil steering signals, hazard warning signals, braking signals, reversing signals, horns, etc. These signals are all sent by the driver to other vehicles and pedestrians according to road traffic conditions, with strong randomness, generally The self-switch control, such as the brake signal, is mostly controlled by the brake pedal linkage: the reverse light is mostly controlled by the gear lever reverse axis linkage, and can be turned on without the driver’s special operation. The horn button is mostly on the steering wheel, so the driver can’t leave his hand. The steering wheel can send out a signal.
1. The turn signal lamp has a certain flashing frequency. The national standard stipulates that it is 60～120 magnets/min. The Japanese stipulation is (85+10) times/min. The power of the turn signal is usually 21～25W, both front and rear, left and right. Large vehicles and cars often There is also a turn signal light on the side. The general connection of the circuit is: the turn signal, turn signal switch and turn flash relay are connected in series with the ignition switch via the normally closed contact of the hazard warning light switch, that is, the turn signal light is used when the ignition switch is in the working position (ON).
2. The hazard warning lights are mainly used in the following situations: the vehicle is malfunctioning or dangerous and cannot be driven: the vehicle has the task of towing other vehicles, and other vehicles are required. Note: The vehicle needs to pass first and the other vehicles need to avoid.
Therefore, the hazard warning light can be used when the engine is not working. At this time, there is no need to switch on the ignition system and the instrument warning light. For this reason, a hazard warning switch is provided. It is a multi-pole linkage switch. When disconnecting the ignition switch wiring, Connect the battery wiring, the flasher and bulb power directly come from the battery, and connect the output end of the flash relay with the left and right turn signals. That is, when the flashing relay is activated, the left and right turn signals and the indicator lights simultaneously send out a hazard signal.
eight . Wiring law of electronic control system
1. Understand the function of the electronic control system, which components are controlled, and which physical quantities are controlled. For example, some control ignition, some control fuel injection, and some control automatic transmission.
2. Master the name, installation location, function, structure principle and main technical parameters of each sensor. For example: the resistance value in the power-off state, the potential and current in the power-on state, to figure out whether the signal voltage of various sensors is an analog quantity, a pulse quantity or a switch quantity.
3. Master the name, installation location, function, structure principle and main parameters of various actuators.
4. Understand the role of the main functional blocks in the computer, and master the serial number, letter code, and normal voltage or resistance between the terminals of the sensors and actuators.
5. Understand the installation position of the computer, each sensor, and each actuator on the car, distinguish the serial number and code of each connector and its terminal, and distinguish the shape characteristics of each component.
6. Understand the fault diagnosis socket or the communication interface of the tester, find the fault code table of each vehicle according to the country, manufacturer and vehicle group, read the fault code with the flashing of the instrument or the fault check lamp, determine the fault location, and eliminate the fault.
The wiring rules of the electronic control system circuit can be summarized as: the computer control circuit must be controlled by the ignition switch, and there must be various sensors to input the working condition signals at any time, for example: magnetic pulse type or Hall type sensors can generate pulse voltage signals: some sensors are Made of a thermistor, the resistance value changes and the output voltage also changes accordingly. It belongs to analog voltage signals, such as water temperature and intake air temperature sensors. The electronic control system actuator is controlled by a computer and has a self-diagnosis function.
Computer work generally consists of two modes-open loop and closed loop control. For example, the open-loop control of fuel injection: After the engine computer receives the input signal, it only responds according to the preset program, and does not monitor the signal of the oxygen sensor. Open loop operating conditions include warm-up operating conditions, deceleration operating conditions, and full throttle operating conditions. Closed-loop control: The engine computer detects the oxygen sensor signal, so that the computer-controlled fuel injection pulse width can obtain the ideal air-fuel ratio to achieve the best fuel economy and low emissions. The closed-loop operating conditions include idling operating conditions, cruise operating conditions, and so on.
Nine, wiring precautions
1. Prepare the circuit schematic diagram of the vehicle to be wired. If there is no circuit diagram, it is best to draw a wiring sketch by yourself against the actual product, which will bring great convenience to the wiring maintenance work.
2. Due to the need for temporary external wiring for maintenance, attention must be paid to insulation to prevent short circuits.
3. Do not connect with live wires. When the wires are damaged, replace them with the wires of the original rules. Be careful in connection and minimize the contact resistance at the connection.
4. After the wiring is completed, it should be tied up according to the original wiring requirements.