Most modern motorcycles use a capacitor discharge ignition system, commonly referred to as CDI. Capacitor discharge ignition relies on the charging and discharging of a capacitor to generate an ignition energy pulse, which is supplied to the primary coil of the ignition system. The high voltage induced in the secondary coil then causes the spark plug to produce a spark. Based on the power source, capacitor discharge ignition systems can be divided into capacitor discharge magneto ignition systems and capacitor discharge battery ignition systems. Figure 1 illustrates the working principle of a capacitor discharge magneto ignition system. The charging coil generates an alternating potential. During the positive half-cycle of the induced potential, the battery charges capacitor C through a half-wave rectifier diode VD1 with pulsating DC current. The thyristor SCR serves as the electronic switch in the CDI system. Its triggering is achieved via the induced pulse from the trigger coil L2. When the magneto flywheel reaches the ignition position, the positive pulse from the trigger coil L2 supplies a triggering current to the gate of the thyristor SCR, causing it to conduct. At the moment the thyristor SCR is triggered, capacitor C rapidly discharges through the anode and cathode of the SCR into the primary coil L3 of the ignition system. This discharge current causes a rapid change in the magnetic flux of the ignition coil, inducing a high voltage in the secondary coil L4, which generates a spark at the spark plug. The capacitor discharge magneto ignition system is simple in structure, cost-effective, and easy to use. However, since it is directly powered by the magneto, the capacitor's terminal voltage is significantly affected by engine speed. The charging energy of the capacitor is insufficient at both low and high speeds, leading to weak ignition energy, difficulties in cold starts, and reduced high-speed performance. To address the issue of insufficient charging energy at low and high speeds, many mid-to-high-end motorcycles adopt a direct power supply DC-CDI system. The DC-CDI ignition system mainly consists of a boost and oscillation circuit and a trigger circuit, as shown in Figure 2. The converter, a small transformer, inverts the 12V battery voltage into a high voltage of around 300V to charge capacitor C. The ignition timing detection circuit controls the ignition advance angle at different speeds, optimizing engine performance. A CDI system with automatic ignition advance adjustment is called ACDI. ACDI is equipped with a device that automatically adjusts the ignition timing based on engine speed, ensuring smoother riding, more complete combustion, and lower emissions. Compared to standard CDI, ACDI significantly enhances motorcycle performance, extends the economical speed range by approximately 96%, improves fuel efficiency by 10%–25%, increases top speed by 10%–25%, and reduces exhaust emissions by 15%–40%.
