The composition and principle of digitally controlled ignition system
Abstract: Taking the single-chip microcomputer as the control core, using the operation and control functions of the single-chip microcomputer, the precise curve control of the engine ignition advance angle is realized, so that the engine works in the most ideal state, and the measured speed and mileage are displayed in real time by the liquid crystal display module. It has changed the traditional ignition mode that the ignition time can not be controlled with the speed of the curve, the best ignition point can not be obtained, and the engine can not perform well at any speed.
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The ignition system plays a very important role in the gasoline engine. The ignition energy must be large enough according to the regulations. Otherwise, the mixture in the cylinder cannot be ignited. The ignition timing or ignition advance angle is one of the important parameters affecting the performance of the engine. The determined engine operating conditions correspond to an optimal ignition advance angle. Too early or too late ignition will directly affect the fuel economy and power of the motorcycle. To this end, it is the design key to obtain the optimal ignition advance angle of the engine through testing and to control the engine to ignite as best as possible.
At present, foreign large-displacement sports motorcycles have begun to use microcomputer control technology. Japan's Honda, Kawasaki, Suzuki, etc. have launched such models, and China is far behind developed countries in the application of ignition advance digital control technology. In fact, the application of this technology in the gasoline engine of the car produced in China has just begun, but it has not been applied on the motorcycle gasoline engine.
1. The composition of the digital control ignition system
The digital control ignition system is mainly composed of a Hall element, a signal shaping circuit, a single chip computing processor, a power amplification high voltage igniter and a liquid crystal display part. The original engine engine is used to collect the working stroke of the engine, and then the signal is processed by the signal processing circuit (signal amplification, waveform transformation and waveform shaping). Since the digital igniter adopts the single-chip control circuit, as long as the optimal ignition advance angle law of the gasoline engine is obtained, the digital igniter guarantees the best ignition. The block diagram of the ignition system is shown in Fig. 1. In the signal processing circuit, the amplifier is used to amplify the acquired signal to meet the amplitude requirement of the digital signal; the waveform transform and the waveform shaping circuit are used to convert the amplified acquisition signal into a TTL signal receivable by the single chip, through the INT0 of the single chip microcomputer. The pin receives, 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, the period of the measured pulse signal), and then calculate the most according to the pulse width. Good ignition angle, the signal is output to the power amplification high voltage igniter to complete the ignition; at the same time, the single chip computer calculates the engine speed according to the pulse period and displays it through the liquid crystal display module.
2, the principle of single-chip control ignition advance angle
Install two motorcycle-specific Hall originals on the engine magneto, one installed at the maximum ignition advance angle position and the other at the top dead center position of the engine piston operation, so that when the MCU collects it, there is 2 reference points. When the engine is just starting, the piston runs at a slower speed and the cylinder pressure is insufficient. Therefore, the cylinder pressure is maximum only when the piston is running to the top dead center after the engine is started. At this time, the ignition is the best time; when the engine works for a while, The ignition timing of the engine will change. The faster the engine runs, the more the ignition advance angle should be increased. Because only the pre-ignition can make the engine have the maximum energy release during the power stroke. If the engine cannot be pre-ignited, the engine will appear weak. The speed of the car cannot be increased; but the advance angle cannot be too large. The advanced angle wastes energy in advance. Some of the work is done with negative work. Therefore, only the precise control of the ignition advance angle can maximize the engine output and minimize energy consumption.
2.1 The choice of working frequency of single chip microcomputer
Because the engine speed can reach 10000r/min when the motorcycle runs at high speed, the ignition advance angle should be the maximum. Due to the different displacement of the motorcycle, the stroke and the cylinder bore of the piston 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 should be ignited at least 2 times every 5°, the frequency of the MCU output is at least: 2×(360/5)×10000=1440000Hz/min; The operating frequency is 12MHz, which fully meets 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 is considered to be ignited at the time of operation, and the igniter controlled by the single-chip microcomputer considers the time when the ignition does not ignite, that is, only a small part of the time is stopped during the operation of the engine. Ignition, as seen from Figure 2, after using the single-chip ignition system, the number of ignition triggers for the ignition stroke and the exhaust stroke is increased, so that the engine mixture is fully burned, and the combustion is not complete, and the spark plug carbon does not work properly. And so on. Moreover, at the time of high-speed operation of the engine, at least six or more ignition processes are guaranteed within the maximum advance angle; high-frequency ignition is continued during the exhaust stroke, the incompletely combusted mixture is sufficiently burned, and the spark plug is cleaned again to complete the high-frequency ignition.
2.3 single chip control ignition advance angle
The engine is collected by using two Hall elements. After amplification and shaping, the shaped signal is input to the single-chip microcomputer, and the single-chip microcomputer analyzes it. The speed of the engine is calculated according to the time difference between the two Hall elements, that is, they are The shorter the time difference is, the higher the engine speed is. At the same time, the liquid crystal display module displays the speed condition, and according to this data, it is analyzed in which area (low speed zone, medium speed zone or high speed zone) the engine works, and the ignition is performed according to different zones. Advance angle control. When the engine is running, the sensors of the engine will monitor the parameters such as load, engine speed, vehicle speed and water temperature, and send them to the computer. After analyzing and processing the information, the corresponding ignition advance angle is calculated by the single-chip microcomputer according to the engine speed.
The biggest advantage of single-chip microcomputer control ignition is that it can comprehensively consider the working condition of the engine. For example, when the engine temperature is too high and the oil quantity is too low, when the vehicle accelerates again, it will cause damage to the engine. At this time, the MCU will automatically perform the igniter. Control, 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 to increase the engine speed is the change of the ignition angle). It has been proved by experiments that Suzuki's 250mL motorcycle will only drive at a speed of 40km/h, and the Honda 400mL motorcycle will only drive at a speed of 55km/h.
In short, the use of a single-chip microcomputer to control the working state of the engine will become an inevitable trend in the future. As the engine uses a smart chip, the engine is automatically analyzed to directly control the engine according to the running condition of the engine and can prevent artificially bad intervention so that the engine can be effectively protected. It is also convenient to install various electronic products such as touch-type code locks, remote controls, clock displays, digital fixed speeds, etc. These functions are easily realized by the MCU.
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