Research On The Electromagnetic Radiation For Lgnition System In Car Engine

With more electric devices installed in cars, cars' security is undergoing increasing challenges. Electromagnetic compatibility technology emerges at this time and can precisely adapt itself to the current development of cars, for it offers effective solutions to solve the compatibility problem among cars'electronic devices. There are a lot of electromagnetic radiation sources in cars, such as motors, relays, switches, and some electronic systems (air conditioning system, GPS, entertainment system, ignition system, etc.), among which the ignition system has the maximum radiation intensity and thus is the most influential one. So the research on the electromagnetic compatibility of the ignition system has a representative significance. The design of the electromagnetic compatibility starts from the subsystem in electronic equipment, ahead of which, through the image of the simulation, the research on the ignition system needs to be applied to predict the possible problems of electromagnetic compatibility. Recently, many scholars are building up the equivalent circuit model in order to analyze and solve the electromagnetic radiation of the system and each device, or through one single way, to suppress electromagnetic radiation separately. The electromagnetic radiation is such a complex issue that mere numerical methods cannot solve the problem and thus cannot produce noticeable effects. In this paper, through the simulation of each component's electromagnetic radiation and the suppression of electromagnetic radiation and experimental analysis, an effective way to improve the electromagnetic compatibility of the ignition system is applied in order to improve the car's electromagnetic compatibility and enhance cars'security.In this paper, the car ignition system of electromagnetic radiation simulation and experimental verification are taken as the technical lines, and the main electromagnetic radiation departments (ignition system, spark plugs, ignition coils, high voltage wires, etc.) on the ignition system are simulated and corresponding improvement solutions and measures are put forward, based on which, by using FDTD method, the electromagnetic radiation source of ignition system is established. In normal working conditions, each component electromagnetic radiation simulation image is obtained by defining boundary conditions of each part and through theoretical analysis, mathematical modeling and experimental verification, measures taken are proved to be feasible and superior. The main tasks are as follows:Based on the prediction theory of the electromagnetic simulation, mechanism of the main electromagnetic radiation devices in the ignition system is analyzed, and the different numerical expressions of field sources are deduced, which are useful for simulation of electromagnetic radiation field source, so the boundary conditions can simulate the actual environment better and the measures taken are more targeted.According to the parts of the ignition system, mathematical models are built and numerical expressions of each component are deduced. The boundary conditions are established in the light of the actual components and the condition for simulating electromagnetic radiation of components. Simulation images are given out by using Matlab, HFSS and EMCstudio. The causes of electromagnetic radiation are analyzed through the simulation. The mutual interference model is established between the high-voltage wire and the common wires, and the crosstalk mathematical images are simulated between them. The acceptance model of the car's antenna is figured out for ignition system. Besides, in order to reduce effects of ignition on antenna, received images of the antenna are simulated to judge the acceptance ability. The model of the spark plug is built up for simulating the electromagnetic radiation image of the middle section and the solenoid model is established for simulation, so space images and profile images are produced.Eelectromagnetic field sources are identified according to electromagnetic simulation for proposing suppression measures. While the switch has strong electromagnetic radiation intensity in the frequency band of 150 KHz, circuits design is taken for filtering serious band interference. At the same time, internal structures can be adjusted in other parts. Since the car is a semi-closed shield, and there are many apertures, common electromagnetic leakages are inevitable. To suppress electromagnetic leakages, several ways like changing apertures shape, improving field source structure and taking circuit design can be adopted. By using diffraction theory, Diffraction field formulas through the aperture are derived and the diffraction field through a rectangular aperture is simulated. Through comparing the electromagnetic shielding effectiveness of the several rules aperture, it can be seen that the smaller the width to length ratio is, the better the shielding effectiveness of rectangular aperture can be. So the rectangular aperture of smaller width to length ratio has better suppression effects. In addition, through aperture of shield, electromagnetic field is simulated, and the result displays that the shielding effectiveness is reduced gradually with the higher frequency.According to the hard and soft devices needed in the experiment, experiment system and technology are designed. Apertures of engine compartment are designed to be Rectangular slot in order to reduce electromagnetic leakage. Because of the suppression measures, the electromagnetic radiation from ignition system is diminished by 9.8dB averagely. It can be seen that the combination of several measures is more effective than single measure.The innovation in this paper is that the combination of several measures is taken to suppress electromagnetic radiation and leakage of ignition system by simulating electromagnetic radiation of device internal structures, and so it avoids solving questions by one single measure. On the basis of the ignition system electromagnetic radiation principle, electromagnetic radiation formulas of the ignition system are derived, and FDTD algorithm is proposed to simplify the PML absorbing boundary conditions. The requirement of space divergence is relaxed toδ<λ/8. Eelectromagnetic field formula is derived through the apertures and Electromagnetic radiation is simulated through the different apertures. The smaller ratio of width and length is, the more weak electromagnetic leakage is in the case of the same area.