Starting from 1957, American companies have introduced an electronically controlled gasoline injection system, which is called EFI for short. EFI technology is the engine, which has created a new era for the development of the whole transportation industry. At first, analog EFI was used, and later it developed into digital EFI. Its basic principle is that the microcomputer (ecu) accurately controls and selects the best ignition and fuel injection timing and fuel injection quantity through analysis, calculation and judgment according to the signals of various sensors. The advantages of electronically controlled gasoline injection are as follows: firstly, the fuel quantity can be optimized most accurately according to specific targets for various working conditions, and the best matching can be achieved in all working conditions; Second, it can realize closing control and prevent the deviation of fuel injection quantity caused by the change of injection density.
In a gasoline engine, the combustible mixture in the cylinder is ignited by electric spark. In the ignition system of automobile engine, the ignition coil is the executive part to provide ignition energy for igniting the air and fuel mixture in the engine cylinder. It is based on the principle of electromagnetic induction. By closing and opening the primary circuit of the ignition coil, the current in the primary circuit increases and then suddenly decreases, so that the high voltage required to ignite the spark plug will be induced in the secondary. The ignition coil can be regarded as a special pulse transformer, which converts the low voltage of 10- 12v into a voltage of 25000v or higher.
Therefore, a spark plug is installed on the cylinder head of the gasoline engine, and the head of the spark plug extends into the combustion chamber. All the equipment that can generate electric spark between spark plug electrodes within a specified time is called ignition system, which usually consists of battery, generator, distributor, ignition coil and spark plug. Used for early mechanical contact circuit breakers (namely platinum ignition) and ignition by mechanical high-voltage distribution cap without distributor transistor.
And later the double spark coil. It belongs to an ignition system controlled by a microcomputer, and is mainly composed of the following components: a sensor for monitoring the running condition of the engine, a microprocessor (ecu) for processing signals, an igniter responding to instructions from the microcomputer, an ignition coil, etc. Because the microcomputer-controlled ignition system is no longer equipped with vacuum centrifugal ignition advance adjustment device, the ignition advance angle is controlled by microcomputer, so that the engine can optimally adjust the ignition time under various working conditions and make the ignition advance to the range where the engine just does not knock. The ignition system controlled by microcomputer has the advantages of low energy loss, good high-speed performance, small electromagnetic interference and high ignition accuracy. At present, it is more and more used in mid-to high-end cars. Distributorless ignition mode is used for simultaneous ignition, that is, two cylinders share one ignition coil, that is, one ignition coil has two high-voltage output terminals.
The ignition system consists of a microprocessor (ecu), an ignition coil, an electronic drive module, a high-voltage ignition wire and a spark plug, as shown in the figure (Note: since there is no schematic diagram of the Liana car, this figure is for reference only).
1. Various sensors 2. Electronic control unit 3 igniter (electronic drive module) 4. Ignition switch 5. 12v battery 6. Ignition coil 7. Spark plug 8. Primary coil 9. Secondary coil.
The following explains the characteristics and working principle of each component:
1, microprocessor (ecu)
The so-called ordinary riders' computer refers to the driving computer, ecu-electronic control unit-electronic control unit, which is responsible for the supervision of vehicles and engines. It consists of an input signal sensor, an electronic control unit (ecu) and an ignition actuator. In other words, the ecu we are talking about is some main sensors, such as engine speed, cooling water temperature, intake air temperature, throttle position, oxygen sensor, intake air pressure and so on. After calculation and processing by ecu, it is sent to the execution unit for correction, so as to realize high-precision air-fuel ratio and optimal ignition timing control. In addition to supplying suitable fuel and adjusting ignition angle and timing according to different driving conditions, ecu must also be responsible for controlling various electronic equipment, such as air conditioning system, cooling system and self-inspection system. For vehicles, ecu is equivalent to the brain of human body, which is responsible for receiving various signals, controlling various systems through built-in basic programs and maintaining the normal running of vehicles. According to the pre-designed program, ecu calculates the information sent by various sensors, and after processing, limits all parameters to the allowable voltage level, and then sends them to relevant actuators to perform various predetermined control functions.
The microprocessor calculates the fuel injection time, fuel injection quantity, fuel injection rate and fuel injection timing based on the input data and the data stored in the map. And these parameters are converted into time-varying electric quantity matching with engine operation. Based on the engine speed and load, after calculation and processing by ecu, the action instruction is sent to the fuel injector, fuel supply pump, etc. , so that each cylinder has the most suitable fuel injection quantity, fuel injection rate and fuel injection timing to ensure the best combustion of each cylinder. Because the work of the engine changes at a high speed, it requires high calculation accuracy and fast processing speed. The performance of ecu should develop with the development of engine technology, and the memory of microprocessor is getting bigger and bigger, and the information processing ability is getting stronger and stronger.
The signal is input to the electronic ignition controller, and after being amplified and shaped by the high-power transistor pre-circuit, it controls the charging and discharging process of the high-energy dry ignition coil primary. When the power tube is turned on, the primary of the ignition coil is also turned on, and the ignition coil stores energy. When the signal turns off the power tube of the controller, the primary of the ignition coil is turned off, and the instantaneous high voltage is induced in the secondary of the coil.
The control signal from the microcontroller is amplified by the power transistor in the igniter. (Note: I have never disassembled the ecu of Liana car. Some cars use power module or Darlington, or directly use microcontroller as the core of ignition electronic control unit, which consists of power supply, input signal shaping, driving amplifier circuit, communication circuit and other functional modules. Either way, the principle is the same. Realize the on-off control of the primary circuit. Namely ignition control: including ignition sequence control, ignition timing control and ignition energy control. The ignition system should be ignited according to the working sequence of the engine, that is, the ignition sequence should be consistent with the working sequence of the engine, otherwise the mixture can not be ignited in time and the engine can not work normally. The purpose of ignition timing control is to make the engine have high power output, low fuel consumption, low knock and low emission. The ignition system must be ignited at the most favorable moment, and the above goal needs to be compromised. The ignition time is expressed by the ignition advance angle, and the crank angle from the spark plug to the piston operation to the top dead center of the compression stroke is called the ignition advance angle. The optimal ignition advance angle of the engine under different working conditions is different. In the ignition system controlled by microcomputer, the working state of the engine is determined according to the signals of sensors such as engine speed and load, and the optimal ignition time is calculated. The microcontroller outputs the control signal, turns off the power transistor and cuts off the primary circuit, thus realizing the control.
2. Ignition coil
In the ignition system of automobile engine, the ignition coil is the executive part to provide ignition energy for igniting the mixture in the engine cylinder. It is based on the principle of electromagnetic induction. By closing and opening the primary circuit of the ignition coil, the current in the primary circuit increases and then suddenly decreases, so that the high voltage required to ignite the spark plug will be induced in the secondary. The ignition coil can be regarded as a special pulse transformer, which converts the low voltage of 10- 12v into a voltage of 25000v or higher. The win current mainly passes through that primary coil and is store as a magnetic field. When the current of the primary coil winding is suddenly cut off (the grounding end of the circuit is disconnected by the power transistor), the magnetic field decays, causing the secondary coil winding to generate induced electromotive force, and the voltage of the induced electromotive force is enough to discharge the spark plug, which is called induced discharge ignition. (pictured). There is also a capacitive discharge ignition system, which is usually called cdi ignition mode.
Our Liana car uses a closed magnetic circuit solid ignition coil, which is mainly composed of a low-voltage coil winding, a high-voltage coil winding connected in series with a high-voltage damping resistor and divided into two outputs, a closed magnetic circuit iron core, a shell and a solid filler (its external structure is shown in the figure).
3. Another component in the ignition coil-high voltage line.
As the name implies, the high voltage conductor is responsible for transmitting high voltage electricity from the high voltage coil to the spark plug. High-voltage lines are actually very simple insulated wires. One of the most common metal wires is covered with high-strength insulator. Its main quality index is that it can have good insulation strength at high and low temperatures. The current it passes through is very small, and the requirements for the metal wires inside are very low; The pass voltage is very high (15000v-40000v), so the insulation coefficient of the insulation material is required to be very high. The main problem is the aging of insulation materials and the decrease of insulation strength, which leads to leakage. An excellent set of high-voltage lines must have minimum current loss to avoid electromagnetic interference caused by high-voltage power transmission. Therefore, the high-voltage ignition wire is designed with resistance, and the circuit is scientifically called damping resistance. The resistance of high-voltage lines varies according to the design of various high-voltage output systems, some are only a few hundred ohms, and some are above 10k. Of course, the high-voltage line with damping resistance is only used in EFI vehicles, and the carburetor car of platinum automobile ignition system does not need to be used here.