| Along with the development of the car industry, the requirement to the enginetechnology becomes higher and higher. It is the core issue of the study to the scientificresearchers that how to improve the engine's fuel efficiency and engine performance. Asfar as gasoline engine is concerned, because of the combustion characteristic of gasolineand characteristics of gasoline engine working principle, during the process ofimproving the engine performance which makes the question that the petrol engineknock has become both inevitable and the outstanding problems which at the same time,severely restricts the engine's performance. In order to solve the problem of the gasolineengine detonation, the first thing to do is testing accurately whether the engine knocksor not, and then is eliminating the detonation. And the best thing is controlling thecritical state between knock and non knock when the engine is working, so the engineperformance and the fuel economy are in the best state. Past means of knockingdetection has the problem of poor precision, high costing, short life, and cannot judgemulti cylinder machine knock cylinder, etc. Because of the shortage of the detectionmeans, the precision of the knocking control system and the improvement of gasolineengine performance are being limited overall.This paper presents the method of knock detection by the spark plug ion flow,which overcomes the shortcomings of other methods, and has high precision, low cost,long service life, and able to realize the single cylinder test when knocking, andprovides a new direction to the development of knock detection. In the paper, we madefurther detailed research according to the detection method, the Influence factors of ionflow signal, the relationship between ion flow signal and engine detonation, and theapplication of wavelet in the ion flow signal analysis process, and then got the relativeconclusions.This paper mainly works in the following aspectsAlthough many scholars and teams involved in the study of ion flow method inrecent years, for the detection means of ion flow was restricted, leading to analysis ofthe ion flow signal has not been able to study further. In order to detect the stable andreliable ion flow signal, firstly, we should optimize the detection circuit of ion flow andcontrol the amplitude of a signal and signal to noise ratio in our satisfactory range, thisis also the precondition of the subsequent signal analysis. And then, we must create theideal, stability experiment conditions that we need in the engine, in order to collect theexperiment data. The work seems simple, it is the foundation of the whole research, andall the following studies base on this work.1. Optimize the signal acquisition circuit of the ion flow and realize the low noiseacquisition of ion flow signal. The signals that are collected in the experimental processare stable, little interference by high pressure and then the system of signal acquisitioncan work very steady. The repeatability of ion flow signal waveform is very good underdifferent engine working cycles, when the engines are in the same work condition,which make a breakthrough in the measurement of ion flow signal.2. Study the problem that the ion flow signal is affected by spark plug parameters. It is very critical that the ion flow affected by spark plug, which is the crossing part ofengine ignition system and ion flow signal acquisition system. In the paper, we drewconclusions by the comparative researching on the ion flow signal from three differentparameters of spark plugs.3. Study the problem of ion flow signal is affected by the value of octane. The ionflow signals are different when the engine using different octane rating of gasoline.When the engine detonation is caused, and then we study the ion flow signal that wecollected in the experiment, and got the range characteristics and range integralcharacter of ion flow signal when using gasoline of low octane rating.4. Study the problem of ion flow signal is affected by the change of offset voltagein the detection circuit of ion flow signal. We need to make it clear that the ion flowsignal is affected by the change of offset voltage thus to control the ion flow signalamplitude and make it meet the requirements of our follow up signal processes. Weanalyse the ion flow signal that is collected under350V and700V offset voltage in theexperiment contrastively and draw conclusions accordingly.5. Study the character of ion flow signal under different degrees of engine knockintensity. The core content of this article is the detection and controls of engine knockby ion flow signal, therefore, we must find out the relationship between the ion flowsignal and the engine detonation, when the engine speed gets1800r/min, we collect theion flow signal respectively when the engine knocks under the condition of21%Throttle Angle (torque about70Nm), of20%Throttle Angle(torque about60Nm),19%Throttle Angle(torque about50Nm),18%Throttle Angle(torque about40Nm).In theprocess of signal analysis, in order to contrast the ion flow signal under circumstancesof knocking and not knocking, we divide the cylinder pressure in sections andput the working cycle together of similar air condition in the cylinder. In differentdriving conditions and points, the segment division base on the cylinder pressure frommore than4MPa to2MPa with0.5MPa for step length. Analyze and contrast the ionflow signal amplitude characteristics respectively in the same section of the cylinderpressure and in different sections and then get the conclusions accordingly.6. Leading in the method of wavelet analysis to the analysis of ion flow signal. Themethod of wavelet analysis is the new method of signal analysis in recent years and thedevelopment and extension of Fourier transform. Combining the characteristic of ionflow signal, the article made wavelet analysis of ion flow signal and get the betterconclusions with the analysis of ion flow signal amplitude.The main innovation points of the paper1. Optimization of the ion flow measuring circuitIt is a important technical problem to the researchers that the optimization of theion flow signal detection circuit. If we cannot cope with the isolation of dozens of kvhigh ignition pressure, we will cannot acquire the data or even burn down theinstrument. In the course of experiment, this problem was thoroughly solved, theinterference to the signal is small, the signal to noise ratio (SNR) can meet therequirements, the signal amplitude can also freely control in the scope of oursatisfaction. 2. In depth study of the question effect of external factors in ion flow signalIt is the important factor to affect ion flow signal that the spark plug parameters,fuel octane, bias voltage of ion flow detection circuit and the other parameters of theoutside world, this paper discusses the influence of external factors in ion flow signalproblem.3. In depth study the question of change rule of ion flow signal amplitude underdifferent knock intensitiesThis thesis proposes the new viewpoint that divided the cylinder pressure intosections, even analyzing ion flow signal based on the division of classification, anddescripting the relationship between the rate of ion flow signal and the detonation indetail.4. Leading the method of wavelet analysis in the analysis process of the ion flowCombined with the characteristics of the ion flow signal, using Hal waveletanalysis in the analysis of ion flow, it has been found that the method of waveletanalysis is a kind of very good methods of signal analysis. It will promote the analysisof ion flow signal on a large scale in the future.The future work prospectsThe work that needs to be further enriched and perfected in this paper mainly is:1. Improve the experimental conditionsDue to the limit of the conditions, most content of this paper used the cylinderpressure sensor to replace the spark plugs doing experiment and data collection. Thereare certain differences between the cylinder pressure sensor and ordinary spark plug, sothe result must be limited. In order to overcome these limitations, the best way isdrilling in the cylinder, installing cylinder pressure sensor and common spark plugseparately. At the same time, installing the common spark plug so as to make the enginework. By using cylinder pressure sensor measuring cylinder pressure variations andcommon spark plug measuring ion flow signal, we could make the experimental resultsmore closer to the true conditon.2. Perform the ion flow test in more working points of the operation conditionIn order to promote the application, we should measure and analysis ion flow inmore working points, and make the experiment results own more universal rules.
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