Design Concept of Single Chip Microcomputer Controlled Motorcycle Ignition Device

The ignition system plays a very important role in gasoline engines. The ignition energy must be large enough as required, otherwise the mixture in the cylinder cannot be ignited; the ignition timing or ignition advance angle is one of the important parameters affecting engine performance. Each given engine operating condition corresponds to an optimal ignition advance angle. Ignition too early or too late will directly affect the fuel economy and power of the motorcycle. Therefore, the key to the design is to obtain the optimal ignition advance angle of the engine through experiments and control the engine to ignite at the best time as much as possible. 

At present, foreign large-displacement sports motorcycles have begun to apply microcomputer control technology. Japanese Honda, Kawasaki, Suzuki and other companies have launched such models, while China lags far behind developed countries in the application of ignition advance digital control technology. In fact, the application of this technology in gasoline engines for cars produced in China has just begun, but it has not yet been applied to gasoline engines for motorcycles. 

1. Composition of digital control ignition system 

The digital control ignition system is mainly composed of Hall elements, signal shaping circuits, single-chip computing processors, power amplifier high-voltage igniters and liquid crystal display parts. The engine Hall original is used to collect the engine working stroke, and then the signal processing circuit (signal amplification, waveform conversion and waveform shaping) sorts the collected signals. Since the digital igniter uses a single-chip control circuit, as long as the best ignition advance angle law of the gasoline engine is obtained, the digital igniter can ensure the best ignition. The block diagram of the ignition system is shown in Figure 1. In the signal processing circuit, the amplifier is used to amplify the collected signal to meet the amplitude requirements of the digital signal; the waveform conversion and waveform shaping circuit is used to convert the amplified collected signal into a TTL signal that can be received by the single-chip microcomputer, and receive it through the INT0 pin of the single-chip microcomputer, so that the INT0 pin can control the operation of the internal timer T0, accurately measure the positive pulse width added to the INT0 pin (that is, measure the period of the pulse signal), and then calculate the best ignition angle according to the width of the pulse, and output the signal to the power amplifier high-voltage igniter to complete the ignition; at the same time, the single-chip microcomputer calculates the engine speed according to the pulse period and displays it through the LCD module.

 

2. Principle of single-chip microcomputer control of ignition advance angle 

Two motorcycle-specific Hall elements are installed on the engine magneto, one at the maximum ignition advance angle position, and the other at the top dead center position of the engine piston. In this way, there are two reference points when the single-chip microcomputer collects data. When the engine just starts, the piston runs slowly and the cylinder pressure is insufficient. Therefore, after the engine starts, the cylinder pressure is maximum only when the piston runs to the top dead center. At this time, ignition is the best time; when the engine has been working for a period of time, the engine ignition time will change. The faster the engine runs, the more the ignition advance angle should be increased, because only by ignition in advance can the engine have the maximum energy release during the power stroke. If it cannot be ignited in advance, the engine will appear weak and the speed cannot be increased; but the advance angle cannot be too large. If the advance angle is too large, it will waste energy, and part of the work will be negative work. Therefore, only by accurately controlling the ignition advance angle can the engine output power be maximized and energy consumption be minimized.  2.1 Selection of the operating frequency of the single-chip microcomputer  Because the engine speed can reach 10000r/min when the motorcycle is running at high speed, the ignition advance angle should be the maximum at this time. Due to the different displacement of motorcycles, the piston travel and cylinder diameter are also different, so the advance angle is also different. The maximum advance angle of the 250mL series is 15°. To ensure that the spark plug is ignited at least twice for every 5° advance angle, the frequency output by the single-chip microcomputer is at least: 2×(360/5)×10000＝1440000Hz/min; while the operating frequency of the ordinary single-chip microcomputer is 12MHz, which can fully meet the requirements. 

2.2 The difference between the new igniter and the ordinary igniter The 

difference between the new igniter and the ordinary igniter is that the ordinary igniter considers when to ignite, while the igniter controlled by the single-chip microcomputer considers when not to ignite, that is, the ignition is stopped only for a small part of the time during the operation of the engine. As can be seen from Figure 2, after using the single-chip microcomputer ignition system, the ignition trigger times of the ignition stroke and the exhaust stroke are increased, so that the engine mixture burns very fully, and there will be no incomplete combustion, spark plug carbon deposition and malfunction. And when the engine is running at high speed, at least 6 ignition processes are guaranteed within the maximum advance angle; high-frequency ignition continues during the exhaust stroke to fully burn the incompletely burned mixture, clean the spark plug again and complete the high-frequency ignition.

 

2.3 Single-chip microcomputer controls the ignition advance angle 

. Two Hall elements are used to collect the engine data. After amplification and shaping, the shaped signal is input into the single-chip microcomputer, which analyzes it and calculates the engine speed at that time based on the time difference between the two Hall elements. That is, the shorter their time difference is, the higher the engine speed is. At the same time, the speed is displayed through the LCD display module, and the engine is analyzed based on this data to determine which area (low speed area, medium speed area or high speed area) the engine is working in, and the ignition advance angle is controlled according to different areas. When the engine is running, the engine sensors will monitor parameters such as load, engine speed, vehicle speed and water temperature, and send them to the computer. After analyzing and processing this information, the single-chip microcomputer calculates the corresponding ignition advance angle according to the engine speed. 

The biggest advantage of using a single-chip microcomputer to control ignition is that it can comprehensively consider the working conditions of the engine. For example, when the engine temperature is too high and the oil level is too low, accelerating will cause damage to the engine. At this time, the single-chip microcomputer will automatically control the ignition device so that the engine can only work in the low-speed zone. No matter how the rider increases the throttle, the engine speed will not increase (because the necessary condition for increasing the engine speed is the change in the ignition angle). Experiments have shown that after being controlled, the Suzuki 250mL motorcycle will only travel at a speed of 40km/h at most, and the Honda 400mL motorcycle will only travel at a speed of 55km/h at most. 

In short, using a single-chip microcomputer to control the working state of the engine will become an inevitable trend in future development. Since the engine uses an intelligent chip, it can automatically analyze and directly control the engine according to the engine's operating conditions and can prevent human adverse intervention, thereby effectively protecting the engine. It can also be convenient to install various electronic products such as touch-type password locks, remote controls, clock displays, digital speed controls, etc. These functions are all easily achieved by single-chip microcomputers.