Automotive ignition function and construction principle

The role of the ignition is based on the ignition signal input signal generator, turn on or off the ignition system of the primary circuit, so that the secondary winding of the ignition coil to produce ignition high voltage. Currently used in automotive ignition internal circuitry in a variety of forms, but the basic function is more or less the same, its circuit is also composed of the corresponding functional circuit, as shown in Figure 5-31. Modern automotive ignition widely used integrated circuits, the internal circuit is very complex. Once damaged, it can only be replaced. Working Principle of Automotive Ignition: The basic working principle of the magnetic induction signal generator and the simplified ignition circuit will be described below. The simplified circuit is shown in Figure 5-32. (1) shutdown protection state: as shown in Figure 5-33, when the ignition switch has just been turned on and the engine is not started, there is no signal voltage from the signal generator, and the battery voltage is divided by R1 and R2 and acted on the P-point, and the P-point voltage is acted on the base of the transistor through the signal coil. This voltage is lower than the conduction voltage of the triode, the triode is in the cut-off state, cutting off the primary circuit of the ignition system. (2) The conduction state of the primary circuit: after the engine is started, the signal generator continuously sends out an AC voltage signal. When the signal voltage is in the direction shown in Figure 5-34, the signal voltage is superimposed with the voltage at point P, so that the voltage at point Q rises, and when the voltage at point Q exceeds the on-state voltage of the triode, the triode turns from the off-state to the on-state, the primary circuit is turned on, and the current flowing through the primary winding of the ignition coil is grounded through the triode. (3) The cut-off state of the primary circuit: when the signal voltage is in the direction shown in Fig. 5-35, the signal voltage is superimposed with the voltage at point P, so that the voltage at point Q is reduced. When the voltage at point Q is reduced to the cut-off voltage of the triode, the triode changes from the on state to the cut-off state, cutting off the primary circuit and inducing a high-voltage electromotive force in the secondary winding of the ignition coil. (4) Constant current control: in order to ensure that the engine can realize stable high-energy ignition under any working conditions, modern cars widely use high-energy ignition coil, the primary winding resistance value is small, generally 0.5 ~ 0.8. After using this ignition coil, the current value of the primary winding is larger. When the engine is running at low speed, the ignition coil passes high current for a long time, which not only wastes electric energy, but more importantly, overheats and burns the ignition coil and electronic components. Therefore, the ignition coil in the ignition has a current-limiting control protection circuit, the purpose of which is to limit the primary current to a certain value and keep it constant, i.e., constant current control circuit. The constant current control principle of the ignition is as follows: as shown in Figure 5-36, VT is the last level of high-power tube of the ignition, Rs is the sampling resistor, and IC is the ignition integrated block. When the value of the sampling resistor is constant, the value of the voltage across the sampling resistor is proportional to the primary current through the ignition coil. When working, the voltage drop value of the sampling resistor is fed back to the current limiting control circuit in the ignition integrated block, so that the current limiting control circuit works to keep the primary current through the ignition coil constant. The specific work process is: when the high-power tube saturation conduction, if the primary current is less than the current limit value, the primary current will gradually increase; when the primary current is higher than the current limit value, the Rs feedback voltage increases the output voltage of the amplifier F, so that VT1 is more conductive, the collector potential is lowered, VT moves to the cutoff region, and the primary current is reduced; when the primary current is slightly lower than the current limit value, the Rs feedback voltage causes the output voltage of the amplifier F to decrease, so that VT1 turns off. voltage decreases, causing VT1 to turn off, the collector potential rises, VT conducts, and the primary current rises. (5) Closing angle control: the closing angle is the angle of rotation of the distributor shaft of the last high power switching tube conduction of the ignition controller, also known as the conduction angle. Figure 5-37 shows the primary current waveform of an ignition with and without a closing angle control circuit. The closing angle control circuit allows automatic control of the conduction time. The angle of closure for various power supplies is as follows: supply voltage (V) angle of closure (°) 11551439163318292026