汽车发动机瞬时转速信号的小波分析

采用小波变换这一工具对瞬时转速信号进行处理。在介绍小波变换基本原理的基础上,对曲轴瞬时转速信号进行了多分辨率分析,即把转速信号分解为多个层次的细节部分和平滑部分。曲轴瞬时转速信号中的噪声被分解到了各层的细节部分,由剩余的平滑部分呆判断发动机的失火和检测各缸工作均匀性,从而为实现失火检测和各缸工作均匀性检测提供了一个新的信号处理方法。     

内燃机各缸功率损失的代理模型诊断方法研究

目前针对内燃机各缸功率损失的诊断方法有很多,但均存在各种局限不能实现实时在线诊断。基于此,在FS诊断方法的基础上提出利用代理模型代替复杂的轴系参数模型的方法并进行功率损失反算,该方法既不需要提取瞬时转速信号的特征故障参数,也不需要复杂的轴系结构参数,仅通过某一测点瞬时转速的各谐次组合就能够精确判断内燃机各缸故障情况,得到满足工程需求精度的诊断结果。通过对比分析反算各缸功率损失与仿真设定功率损失的结果表明:两者相差甚小,完全能够用于工程实际的故障诊断。该方法为快速在线诊断内燃机各缸功率损失提供参考。     

基于瞬时转速的柴油机早期弱故障诊断实验研究

瞬时转速蕴含了大量柴油机运行状态信息,已经成功用于失火严重故障的诊断,但对于早期弱故障的诊断尚缺乏进一步的研究。针对6-135型柴油机,通过在不同程度上调整气缸喷油量、调整气阀间隙、模拟气阀泄漏等方法模拟柴油机早期故障,在不同工况下进行实验数据采集,计算柴油机瞬时转速信号,并分析其不同状态下的变化规律。发现柴油机瞬时转速信号可以用于判断多种早期故障,各缸瞬时转速升程归一化比值P是较直接的特征参数。正常状态下,各缸瞬时转速P值在0.9~1.1以内,若某缸升程P值下降超过10%,可认为该气缸存在故障。该方法对于影响缸内压力的故障如各气缸喷油量不均匀、气阀泄漏等比较敏感,对于活塞-缸套间隙过大等对缸内压力影响程度小的故障不敏感。     

起动电流在发动机气密性检测中的应用

针对传统的发动机气密性检测需要拆卸发动机的缺点,提出了一种基于起动电流的不解体实车在线检测方法.在对发动机不供油起动阶段各缸工作行程、起动阻力矩、瞬时转速、电压和电流的变化规律及相互关系进行了理论建模后,通过柴油机智能检测节点同步采集的实测信号验证了理论模型的正确性.针对F3L912型柴油机提取工作相位难的问题,采用压缩上止点指数来定位压缩行程上止点,进而实现故障缸的定位,并引入了归一化的气缸密闭性参数来判断气缸密闭一致性.在对正常、轻微漏气及严重漏气3种工况下提取的参数进行分析后,证实了提取的参数能够有效区分这些工况.本研究方法在实车在线不解体的情况下实现了发动机气密性故障的定性、定缸和定量判断.     

基于神经网络和瞬时转速的发动机失火故障研究

针对发动机在实际运行中经常会出现单缸或者多缸失火这种典型的故障现象,从发动机瞬时转速的角度出发,对发动机气缸受力与发动机曲轴瞬时转速之间的关系进行了理论研究,建立了其数学模型,利用Matlab仿真软件对瞬时转速曲线进行了仿真,确定并提取出了特征参数,比较了正常情况下和单缸不点火情况下瞬时转速曲线及其特征参数的变化,并把这些变化作为下一步诊断发动机失火故障的判断依据;最后,建立了一个BP神经网络并对其进行训练,同时把仿真数据和实例数据输入到网络中进行了理论验证和实例验证。研究结果表明,发动机的失火故障与发动机瞬时转速之间存在一定的关系,利用瞬时转速可以对发动机失火故障进行诊断;利用BP神经网络方法诊断发动机失火故障具有速度快、效率高的特点。     

扭矩法诊断柴油机动力装置故障

为了探索柴油机的故障机理,对6160A柴油机在正常情况下和一缸熄火时的瞬时扭矩进行了仿真计算,并利用该动力装置分别在活塞环故障、一缸停油、进气故障及正常情况下测录了不同转速和负荷下轴系上的扭矩动态变化信号。分析结果表明,故障原因与扭矩信号之间存在一定对应关系,结合其他传感器信号,可有效、实时地在线诊断柴油机故障。该轴扭测试分析系统也可用于柴油动力装置的实时监测。     

基于多参数融合核电EDG在线监测分析技术研究

针对目前核电应急柴油发电机组现有监测信息难以有效定位故障源的现状,提出一种基于键相、瞬时转速和振动等多参数融合的在线监测分析技术。对数据进行高速连续采集和处理,将时域信号转换至角域以消除转速波动的影响。基于柴油机故障特性和信息融合理论,提取各工作循环相关测点的多特征参数,确定各故障类型与相关特征的映射关系,依次融合相关参数对故障进行分析定位。结合该技术对启动超时故障进行分析,验证了该技术的有效性。     

气体发动机进气管流动特性分析

为研究气体发动机进气管内流体流动特性,以某型气体发动机的进气管道为研究对象,利用Fluent软件对预处理好的三维模型进行仿真计算,得到混合均匀性分布情况及进气管中的流场分布。对进气管中的流场进行分析,结果表明:混合器结构和弯管曲率对进气管内压力分布有着重要影响,进而影响各缸均匀性。对混合器和弯管结构参数进行优化,可使各缸进气均匀性得到改善。     

直列六缸发动机进气歧管CFD分析及优化

直列六缸发动机广泛使用于前置后驱的汽车中,具有顺畅的动力输出性能,且平衡性突出。进气歧管的气道结构对发动机各缸进气量和整体的进气均匀性有着重要的影响,直接影响发动机在不同工况下的工作性能。利用GTPOWER软件和STAR-CCM+软件对某直列六缸汽油发动机进气歧管的内流场进行了数值模拟,并对该进气歧管的进气不均匀性及压力损失进行了分析,通过CFD仿真计算展现进气歧管气道内部流场分布,得到了在某一工况下各个气道歧管的流速图和压力图,得出其结构上的不足,并对气道结构进行优化,从而降低进气压力损失并且保证了各缸进气均匀性。     

基于人工神经网络的柴油机失火故障诊断

车载诊断系统在诊断失火故障时,采用基于曲轴段角加速度和阈值规则相结合的方法,该方法在内燃机高速轻载运行时诊断单缸完全失火工况存在一定的局限性。通过对比分析失火和正常工况下曲轴瞬时转速的幅频和相频特征,提取不同谐次的幅值和相位信息,结合人工神经网络作为故障模式识别工具,得到了一种改善方法。通过台架实验,对此改善方法进行了单缸完全失火、两缸完全失火和单缸一定程度失火的故障诊断测试。结果表明,在实验条件下该方法可以有效识别不同的失火模式,并可在单缸失火模式下实现失火程度判别。同时,该方法通过少量工况数据训练神经网络,即可实现一定转速范围内的失火诊断,可行性强,可用于发动机失火故障在线诊断。     

Misfire and compression fault detection through the energy model

This article proposes a simple algorithm for misfire detection in reciprocating engines. The algorithm, based on an energy model of the engine, requires the measurement of the instantaneous angular speed. By processing the engine dynamics in the angular domain, variations in the working parameters of the engine, such as external load and mean angular speed, are compensated. A dimensionless feature has been abstracted for evaluation of the combustion as well as compression process of each cylinder. The proposed technique is expected to be easy to implement and to provide useful information for on-line monitoring of the in-cylinder processes in an internal combustion engine.     

Torsional system parameter identification of internal combustion engines under normal operation

For internal combustion engines, lumped-mass models of the crankshaft system are frequently used for torque estimation in control and diagnostic applications, such as cylinder balancing and misfire detection. Due to inherent model uncertainties and changing system dynamics it may be necessary to adapt the model parameters from time to time in order to preserve the required model accuracy. In this paper a frequency-domain method for on-line identification of the parameters describing the torsional dynamics of internal combustion engines is presented. In the proposed method, the engine is excited by adjusting the cylinder-wise injected fuel amounts, and the measured responses in torsional vibration frequency components are used for parameter estimation. As the fuel-injection adjustments can be determined in such a way that the net indicated torque is unaffected, the identification can be performed on-line without disturbing normal engine operation. The procedure can be applied to estimate the torsional stiffness and damping parameters of the flexible coupling connecting the engine and the load. In addition, the gains which describe how the cylinder-wise fuel injections affect the amplitudes of relevant torsional vibratory frequency components are obtained. The parameter identification method is successfully evaluated in full-scale engine tests on a 6.6 MW six-cylinder medium-speed common-rail diesel engine.     

Multivariate statistical analysis strategy for multiple misfire detection in internal combustion engines

This paper proposes a multivariate statistical analysis approach to processing the instantaneous engine speed signal for the purpose of locating multiple misfire events in internal combustion engines. The state of each cylinder is described with a characteristic vector extracted from the instantaneous engine speed signal following a three-step procedure. These characteristic vectors are considered as the values of various procedure parameters of an engine cycle. Therefore, determination of occurrence of misfire events and identification of misfiring cylinders can be accomplished by a principal component analysis (PCA) based pattern recognition methodology. The proposed algorithm can be implemented easily in practice because the threshold can be defined adaptively without the information of operating conditions. Besides, the effect of torsional vibration on the engine speed waveform is interpreted as the presence of super powerful cylinder, which is also isolated by the algorithm. The misfiring cylinder and the super powerful cylinder are often adjacent in the firing sequence, thus missing detections and false alarms can be avoided effectively by checking the relationship between the cylinders.     

Effect of Initial Cylinder Liner Honing Surface Roughness on Aircraft Piston Engine Performances

Reciprocating piston engines are the major propulsion devices for light aircrafts, helicopters, and essentially all automotive vehicles. They are expected to fulfil both present-day and future demands for engine performance, durability, fuel economy, and exhaust emissions legislation. One of the key factors related to these demands is the need to the limit thermomechanical internal losses, wear, and lubricating oil consumption, which are in turn conditioned by the tribological behavior of the piston–cylinder assembly. Consequently, this latter system requires a multi-directional approach in terms of manufacturing. Apart from various modifying techniques (e.g. laser texturing), a conventional plateau-honing operation is still the standard technology for shaping cylinder liner surface microstructure. This paper describes the distinctions between variations in the performance of the engines in relation to cylinder liner roughness parameters due to different honing settings. Five air-cooled reciprocating aircraft engines (FRANKLIN 4A-235-B31) served as the objects of research. The engines passed durability tests on the dynamometer bed, including operation under artificially intensified wear conditions. The results show a significant impact of the brand-new honed cylinder liner surface microstructure on the engine output parameters. Detailed study proves that some of the cylinder liner roughness parameters, specifically, the slope of the root mean square line (RMS) for valley roughness Rvq and the linear triangle area for valleys A2, are strongly correlated with the engine operational properties. Higher values of Rvq and A2 are associated with an improvement in engine performance but result in a deterioration in the exhaust harmful emission.     

汽车发动机瞬时转速测量中的噪声分析及补偿方法

对汽车发动机的瞬时转速信号中的量测噪声进行补偿。试验测量结果表明,由飞轮齿圈的齿形误差引起的噪声是瞬时转速信号中的主要噪声源。并且该噪声的幅值与发动机的平均转速成正比。由于这种噪声的频带与飞轮瞬时转速信号物频带可能重叠,因此采用传统的滤波等方法无法完全肖除齿形误差引起的噪声,提出采用２个传感器的补偿新方法,可将齿形误差引起的噪声从瞬时转速信号中消除,试验结果验证了该方法的可行性,训利用瞬时转速检测     

Model-based diagnosis of large diesel engines based on angular speed variations of the crankshaft

This work aims at monitoring large diesel engines by analyzing the crankshaft angular speed variations. It focuses on a powerful 20-cylinder diesel engine with crankshaft natural frequencies within the operating speed range. First, the angular speed variations are modeled at the crankshaft free end. This includes modeling both the crankshaft dynamical behavior and the excitation torques. As the engine is very large, the first crankshaft torsional modes are in the low frequency range. A model with the assumption of a flexible crankshaft is required. The excitation torques depend on the in-cylinder pressure curve. The latter is modeled with a phenomenological model. Mechanical and combustion parameters of the model are optimized with the help of actual data. Then, an automated diagnosis based on an artificially intelligent system is proposed. Neural networks are used for pattern recognition of the angular speed waveforms in normal and faulty conditions. Reference patterns required in the training phase are computed with the model, calibrated using a small number of actual measurements. Promising results are obtained. An experimental fuel leakage fault is successfully diagnosed, including detection and localization of the faulty cylinder, as well as the approximation of the fault severity.     

Design approach for single piston hydraulic free piston diesel engines

The operating characteristics of a single piston hydraulic free piston diesel engine differ significantly from conventional diesel engines and this provides a theoretical basis for controlling and optimizing the design of the engine. The design of the proposed engine intended as a power supply for a hydraulic propulsion vehicle is presented. An engine performance forecast model was generated in AMESim. The performance of the prototype engine is predicted and the predictive results are verified with experiments. The particular features of the engine are discussed. The dynamic characteristics of the prototype engine are analyzed and the results indicate the rationality and feasibility of the engine design parameters. The features of the controllable working frequency and the intermittence output flows are provided. The flow capacity characteristics of the hydraulic valves on the prototype engine are offered. The methods for starting and the operation after misfire are presented.     

Design approach for single piston hydraulic free piston diesel engines

The operating characteristics of a single piston hydraulic free piston diesel engine differ significantly from conventional diesel engines and this provides a theoretical basis for controlling and optimizing the design of the engine. The design of the proposed engine intended as a power supply for a hydraulic propulsion vehicle is presented. An engine performance forecast model was generated in AMESim. The performance of the prototype engine is predicted and the predictive results are verified with experiments. The particular features of the engine are discussed. The dynamic characteristics of the prototype engine are analyzed and the results indicate the rationality and feasibility of the engine design parameters. The features of the controllable working frequency and the intermittence output flows are provided. The flow capacity characteristics of the hydraulic valves on the prototype engine are offered. The methods for starting and the operation after misfire are presented.     

Theoretical Analysis of Piston-Ring Lubrication Part I—Fully Flooded Lubrication

A one-dimensional analysis for lubrication between the piston ring and cylinder wall has been developed. A fully flooded inlet condition and axisymmetric geometry are considered. The piston ring is treated as a reciprocating, dynamically-loaded bearing with combined sliding and squeeze motion. A system of two nonlinear differential equations is used to model the lubrication including the Reynolds cavitation boundary condition. A numerical procedure is then developed to obtain the cyclic variations of film thickness, frictional force, power loss, and oil flow across the ring.

Results are presented for a typical automotive engine. The effects of ring profile, ring tension, and engine speed are examined. It is shown that this analysis can be used to study the influence of ring design parameters in order to improve the design of the ring pack in reciprocating engines.