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1. Capacitor discharge magneto ignition system
07/09/2022
After VD1 half wave rectification, the capacitor C is charged with pulsating DC current. Thyristor SCR is an electronic switching element of CDI. Its trigger conduction is realized by the induction pulse of trigger coil L2. When the flywheel of the magneto turns to the ignition position, the positive pulse of trigger coil · L2 provides trigger current to the control electrode of thyristor SCR, so that the thyristor SCR triggers conduction. At the moment when the thyristor SCR is triggered and turned on, the capacitor C is rapidly discharged to the primary coil L3 of the ignition coil through the thyristor anode and cathode. The discharge current rapidly changes the magnetic flux of the ignition coil, induces high-voltage electricity on the secondary coil L4, and causes the spark plug to generate sparks.
The capacitor discharge magneto ignition system has the advantages of simple structure, low price and convenient use. However, due to the direct power supply of the magneto, the terminal voltage of the capacitor is greatly affected by the engine speed, and the charging energy of the capacitor is insufficient at low speed and high speed, resulting in weak ignition energy, which is easy to cause difficulties in cold starting and degradation of high-speed performance. In order to solve the problem of insufficient charging energy of capacitors at low speed and high speed, many middle and high-grade motorcycles adopt direct current CDI (DC-CDI) with direct power supply.
2. Capacitor discharge battery ignition system (DC-CDI)
The DC-CDI igniter is mainly composed of boost circuit, oscillation circuit and trigger circuit, as shown in Fig. 2. The converter is a small transformer that inverts the 12V voltage of the battery into a high voltage of about 300V to charge the capacitor C. The ignition time detection circuit controls the ignition advance angle at different rotational speeds to make the engine work in the best state. CDI with the function of automatically adjusting ignition advance angle is called acdi. Acdi is equipped with a device that automatically adjusts the ignition advance angle. The ignition timing can be adjusted automatically with the change of engine speed, so that the motorcycle can run more smoothly, burn more completely, and emit more environmentally friendly.
Compared with ordinary CDI, acdi can greatly improve the power performance of motorcycles and expand the economic speed range by about 96%; Save fuel by 10% - 25% and increase the maximum speed by 10% - 25%; Exhaust pollution is reduced by 15% - 40%.
2、 Inductive discharge ignition mode
The inductive discharge ignition mode generates pulses by disconnecting the primary circuit of the ignition coil, induces high voltage in the secondary coil, and causes the spark plug to generate sparks. This ignition method is also called transistor ignition system because it uses triode as switching element. Fig. 3 is the working principle diagram of the inductive discharge battery ignition system. Close the ignition switch ― K, the triode vtr (R is the subscript) is on, and the current flows from the battery to the primary winding of the ignition coil, L1. When the engine is started, the pulse coil L3 generates an AC signal Р When the point is in the + direction, the triode vtr (R is the subscript) remains conductive; about Р When point P is in one direction, the triode vtr (R is the subscript) is turned off. In this way, the current of the primary winding L1 is cut off, the magnetic flux of the ignition coil changes rapidly, and high-voltage electricity is generated in the secondary windings L2, so that the spark plug generates sparks.
