What is the composition and working principle of automobile ignition system?

When the gasoline engine is working, the combustion of the mixture is controlled by the ignition of the spark plug. The function of the ignition system is to provide high-voltage electricity with enough energy to the spark plug at a suitable time according to the working state and sequence of the engine, so that sparks can be generated between its electrodes, ensuring that the mixture can be ignited and the engine can do work.

Ignition system is the system with the highest failure rate among all systems of gasoline engine.

The technical condition of the ignition system not only seriously affects the power, economy and emission performance of the engine, but also determines whether the engine can work normally.

Insufficient ignition energy or no ignition will make it difficult for the engine to work, or even fail to work in serious cases. If the ignition time is not suitable, the engine power will decrease, the fuel consumption will increase and the engine temperature will rise if the ignition time is too late. The ignition time is too early, which leads to engine knocking and even parts damage.

Basic composition of engine ignition system

Power supply: generally composed of storage battery and generator, it is mainly used to provide the required electric energy for the ignition system.

Sensor: It is used to detect various working parameters of the engine and provide ECU with signals needed for ignition control.

ECU: It is the center of electronically controlled ignition system. Igniter: the executive part of electronic ignition.

Ignition coil: stores the energy required for ignition and converts the low-voltage electricity provided by the power supply into high-voltage electricity of 15 ~ 20kV enough to generate a breakdown spark between electrodes.

Distributor: According to the ignition sequence of the engine, the high-voltage electricity generated by the ignition coil is transmitted to the spark plugs of each cylinder in turn.

Spark plug: use the high-voltage electricity generated by the ignition coil to generate sparks to ignite the mixture in the cylinder.

Working principle of engine ignition system

When the engine is working, the ECU determines the best ignition advance angle and power-on time according to the signals received from various sensors and the relevant programs and data stored in the memory, and sends instructions to the igniter accordingly. The igniter controls the on-off of the primary circuit of the ignition coil according to the instruction. When the circuit is connected, current flows through the primary circuit in the ignition coil, which stores ignition energy in the form of magnetic field. When the primary circuit is cut off, a high induced electromotive force (15 ~ 20kV) is generated in the secondary coil, which is sent to the spark plug of the working cylinder through the distributor or directly.

In the electronic ignition system, the G signal generated by the camshaft position sensor and the Ne signal generated by the crankshaft position sensor are used as the main control signals. Based on the G signal, an ignition control signal (IGt signal) with a given crank angle is generated by dividing the frequency by 1.

(1) G signal: it refers to the judgment signal that the piston moves to the top dead center position, and it is a pulse signal obtained by shaping and converting the signal generated by the camshaft position sensor. When the engine is working, the ECU can accurately calculate the time taken for the crankshaft to rotate 1 according to the G signal, and according to the input signals of other sensors, the ECU can determine the ignition advance angle and the energization time of the ignition coil according to the control model in its memory.

(2) Ne signal: refers to the crankshaft angle signal of the engine, which is a pulse signal obtained by shaping and converting the signal generated by the crankshaft position sensor. In electronically controlled ignition system, Ne signal is mainly used to measure ignition advance angle and power-on time.

(3) IGt signal: It is the switch control signal sent by ECU to the power transistor in the igniter.

(4) IGf signal: it is the ignition confirmation number transmitted by the igniter to the ECU after the ignition is completed.