计及活塞销间隙的内燃机曲柄连杆机构动力学分析

基于活塞销与衬套间隙的冲击函数模型和计算多体动力学的方法,研究了活塞销间隙对内燃机活塞-连杆-曲轴运动系统动力学特性的影响。使用冲击函数方法构建了活塞销与衬套的间隙碰撞模型,建立了某单缸内燃机活塞、连杆和曲轴的三维实体模型及内燃机活塞-连杆-曲轴的多体动力学模型。在刚性和弹性两种不同连杆模型下,通过分析活塞运动的速度和加速度,以及活塞销的运动轨迹等研究了活塞销间隙产生的碰撞特性对系统动力学行为的影响。结果表明,间隙的存在对该运动机构有显著影响,在上下止点附近活塞的加速度出现许多由碰撞产生的峰值。     

类金刚石涂层结构对活塞销耐磨特性的影响

为了提高活塞销表面类金刚石(DLC)涂层的结合力及抗磨损性能,使用扫描电子显微镜、圆度仪、粗糙度仪等检测设备对2种活塞销DLC涂层表面、截面及涂层结合处的微观形貌、组成元素和成分进行了对比分析,并对2种活塞销进行了发动机台架耐久试验。结果表明:原样件活塞销耐久试验后涂层大面积脱落且磨损严重,通过改变工艺参数将原样件活塞销进行优化,优化后的活塞销DLC涂层表面的均匀性、平整性及光滑度都有了明显改善,涂层厚度由1.08μm增加到了1.49μm,且粗糙度Ra值由原样件的0.369μm减小为0.144μm,同时圆柱度也明显减小,耐久试验后涂层完好,没有发生脱落。此研究为提高活塞销表面质量,改善活塞销在工作中的磨损及失效提供了参考。     

连杆衬套的开裂分析

机车280型柴油机连杆衬套在使用过程中发生开裂,采用宏观观察、扫描电镜分析、组装工艺分析、受力分析以及金相检验等方法对开裂的连杆衬套进行了综合分析。结果表明,连杆衬套的装配工艺不合理,造成衬套与活塞销高点接触而产生应力集中,这是导致连杆衬套开裂的原因。定位销位置设计不合理以及衬套基体存在严重的疏松,是促使连杆衬套开裂的主要因素。     

轿车活塞衬套材料的组织相研究

活塞衬套材料是发展汽车发动机技术的关键材料。就轿车活塞衬套材料铜合金60Cu-Zn-Si在200℃、400℃、600℃、800℃进行固溶处理，确定材料在不同温度对应的相组成，对处理后的试样进行了SEM和X-ray分析研究，结果表明，该材料的基体相为Cu12.75SiZn292的化合物，结晶度好。     

活塞销失效原因分析

某发动机活塞销失效导致发动机损毁.采用磁粉探伤、宏微观断口分析、化学成分、金相组织及硬度分析等方法对失效的活塞销进行了分析,同时还对活塞销在服役过程中的应力状态进行了有限元模拟计算.结果表明,导致活塞销疲劳断裂的原因是活塞销端面存在磨削裂纹.     

活塞二阶运动对非道路高压共轨柴油机振动及噪声影响分析

活塞敲击是柴油机主要的振动和噪声源,其主要原因是活塞在其与缸套的间隙中做横向和偏摆的二阶运动,因此研究活塞设计参数对活塞二阶运动的影响,优化活塞动力学特性,对于发动机减振降噪具有重要意义。以某非道路四缸高压共轨柴油机为研究对象,建立活塞动力学计算模型以及整机多体动力学计算模型,通过机体和曲轴的模态试验,验证了有限元模型的准确性;采用正交设计方法,研究了活塞销偏置量、活塞裙部中凸点位置、配缸间隙对活塞动力学、整机振动与噪声的影响。研究结果表明:活塞配缸间隙对活塞敲击能量、活塞敲击力、活塞所受力矩影响最大;对发动机振动噪声敏感性分析显示,活塞销偏置是影响发动机振动与噪声性能的关键因素。     

发动机磨损诊断的神经网络技术研究

目的：利用神经网络技术诊断发动机的磨损故障，研究神经网络技术应用于机械故障诊断领域的发展方向，方法：基于油液分析技术，对发动机常见磨损故障进行诊断，具体包括发动机磨损颗粒的识别，磨损元素浓度值的预测和磨损故障智能诊断专家系统，结果：对其于油液分析的发动机故障诊断提供了新的方法，结论：使用神经网络技术可以大大提高发动机磨损故障诊断的效率，说明该技术方法在发动机磨损故障诊断领域是有效的，同时对其它机械设备的磨损故障诊断具有借鉴意义。     

WJ5AI发动机中央传动锥齿轮组件故障分析及改进措施

通过对ＷＪ５ＡＩ发动机中央传动锥齿轮组件故障进行调查、分析，阐明了原中央传动锥齿轮组件结构设计存在不安全因素。中央传动锥齿轮与轴的配合紧度小，圆柱销在变化载荷作用下传递扭矩，与其孔的配合表面产生微动磨损，微动磨损进一步发展造成了中央传动锥齿轮组件传扭失效。     

基于Teager算子的柴油机活塞-气缸磨损故障特征增强方法

柴油机活塞与气缸磨损情况是判断柴油机技术状态的主要指标,也是柴油机大修送修的主要条件,其监测诊断一直是柴油机维修的重点。由于柴油机结构复杂,工作状态激烈,活塞-气缸磨损故障很难有效监测诊断,尤其是活塞-气缸早期磨损故障,更是监测诊断一直是研究的重点和难点。根据活塞-气缸磨损后在工作中产生冲击的特点,利用Teager算子提取瞬态冲击信号的优势,对柴油机怠速时缸体上部左侧振动信号进行Teager算子增强,通过提取出的Teager算子能量最大值,判断是否存在活塞-气缸磨损故障以及故障的严重程度。通过两种不同型号柴油机、不同故障缸的机体振动实测信号分析表明,该方法简便有效。     

发动机磨损诊断的神经网络技术研究

目的　利用神经网络技术诊断发动机的磨损故障 ,研究神经网络技术应用于机械故障诊断领域的发展方向 .方法　基于油液分析技术 ,对发动机常见磨损故障进行诊断 ,具体包括发动机磨损颗粒的识别、磨损元素浓度值的预测和磨损故障智能诊断专家系统 .结果　对基于油液分析的发动机故障诊断提供了新的方法 .结论　使用神经网络技术可以大大提高发动机磨损故障诊断的效率 ,说明该技术方法在发动机磨损故障诊断领域是有效的 ,同时对其它机械设备的磨损故障诊断具有借鉴意义     

Determination of breakdown rates and defect densities in SiO2

Breakdowns in SiO₂ have been classified as defect related, due to wear-out and intrinsic. However, techniques to ascertain defect densities and breakdown rates at defects have not been available, nor has the distinction between wear-out and defect- related or intrinsic breakdowns been clearly demonstrated. A particular problem has been the inability to distinguish defect types, i.e. defects having different breakdown rates. Another source of confusion has been the tacit assumption that breakdown field histograms obtained from ramp breakdown tests are independent of the ramp rate, which cannot be valid for finite breakdown rates. We obtained relationships specifying the statistics of breakdown, including the effect of defects. These actually derive from results describing a Markov death process and depend on the time integrals of breakdown rates in defect-free regions and at defects and on parameters describing the defect distributions. For Poisson distributions of the defect, these parameters are the mean number of defects per device for each defect type. Any breakdown test is described by the same relations since the nature of the test enters only through the time integral of the breakdown rates. If a wear-out mechanism is operative, then the breakdown rates will depend on the time explicitly, i.e. not only via the time dependences of the applied field and temperature. procedures for obtaining defect densities and breakdown rates follow from the derived dependence on these quantities of the expectation value of the fraction of devices broken down. Ramp tests at various ramp rates are advantageous for this purpose. The field dependence of the breakdown rates can be extracted directly from the experimental data and no a priori form for this dependence need be assumed. Experimental results obtained from multiple ramp breakdown tests will be presented. The field dependence of the breakdown rates is found to vary significantly from a simple exponential dependence. Following Klein, the effect of fluctuations on the breakdown rates will be considered qualitatively to rationalize their observed field dependence. No explicit time dependence of the breakdown rates is indicated over the range of field covered by the data, implying the absence of wear-out.     

Dielectric breakdown of an unpoled piezoelectric material with a conductive channel

The dielectric breakdown of an unpoled piezoelectric ceramic, PZT807, with a conductive channel, is investigated. Cylindrical bar specimens with a conductive channel are used for breakdown tests of the unpoled piezoelectric ceramic under purely electrical loads. Narrow tubular channels emanating from the head of the initial channel are observed in the specimens after breakdown occurs. The radius of the tubular channel that is created at the surface of the initial channel head is insensitive to various types of channel formation. The problem of a fine tubular channel that emanates from the initial channel head is numerically solved to evaluate the three-dimensional J integral, which is directly related to the energy that is available at breakdown, at the initiation of a new channel in the specimen. The critical J integral at the onset of breakdown is obtained.     

Multi-harmonic test setup for RF breakdown studies

A multi-harmonic asymmetric cavity is predicted to obtain lower RF breakdown probability than a conventional pillbox cavity, when driven by two or more external RF harmonic sources. Experimental efforts are underway to study RF breakdown in a bimodal asymmetric cavity powered by dual frequency test stand. Details of design of the test stand are described.     

污秽溶液对生物可降解聚乙烯绝缘破坏的影响

采用生物可降解聚乙烯薄膜为试样,考察了污秽程度对绝缘破坏的影响,通过单筒连续变倍视频显微镜对破坏痕取像,利用图像模式识别计算破坏面积与盒子维数,同时与高密度聚乙烯的绝缘破坏特性进行对比,结果表明:生物可降解聚乙烯的击穿电压随污秽程度的加剧而降低,但高于高密度聚乙烯的击穿电压;破坏面积与盒子维数随污秽程度的加剧而减小,但低于高密度聚乙烯的破坏面积与盒子维数.     

Optimization redundancy allocation problem with nonexponential repairable components using simulation approach and artificial neural network

Redundancy allocation is one of the adopted approaches that is used by system designers to improve the performance of systems. In this article, a new model and a novel‐solving method are provided to address the nonexponential redundancy allocation problem in series‐parallel systems with repairable components based on optimization via simulation approach and artificial neural network technique. Despite the previous researches, in this model the failure and repair times of the each component were considered to have nonnegative exponential distributions. This assumption makes the model closer to the reality where most of used components have greater chance to face a breakdown in comparison to new ones. The main aim of this research is the optimization of mean time to the first failure of the system via allocating the best redundant components for each subsystem. Since this objective function of the problem could not be explicitly mentioned, the simulation technique and artificial neural network were applied to model the problem, and different experimental designs were produced using design of experiment methods. To solve the problem, some metaheuristic algorithms were integrated with the simulation method. Several experiments were performed to test the proposed approach, and as the results show, the proposed approach is much more real than previous models, and also the near optimum solutions are promising.     

SOM-BP复合神经网络在齿轮箱故障诊断中的应用研究

针对齿轮箱的故障模式和特征量之间复杂的非线性关系，采用SOM-BP复合神经网络，引用齿轮箱常见的故障及其相关参数作为训练样本建立诊断模型。在Matlab环境下，通过仿真试验并与BP网络进行比较，验证了此复合神经网络用于齿轮箱故障诊断的正确性和精确性，具有一定的工程应用价值。     

多巴胺改性BaTiO_3对BaTiO_3/PVDF复合材料击穿场强的影响

为了提高BaTiO3/PVDF复合材料的击穿场强。首先,利用多巴胺对BaTiO3进行表面功能化处理,得到多巴胺改性的BaTiO3(Dopa@BaTiO3);然后,将其与聚偏氟乙烯(PVDF)混合,采用液相浇铸法制得Dopa@BaTiO3/PVDF复合材料;最后,测量了不同Dopa@BaTiO3添加量的Dopa@BaTiO3/PVDF复合材料的击穿场强和介电性能。结果表明:与改性前的BaTiO3/PVDF复合材料相比,Dopa@BaTiO3/PVDF复合材料在击穿场强显著提高的同时,介电常数基本保持不变;当Dopa@BaTiO3添加量为3vol%时,击穿场强为210kV/mm,比改性前的复合材料的提高了78%;当Dopa@BaTiO3添加量为10vol%时,击穿场强为180kV/mm,比改性前的合材料的提高了88%。研究解决了BaTiO3/PVDF复合材料击穿场强较低的问题,可为同时提高复合材料的介电常数和击穿场强提供参考。     

A decomposition-based approach to flexible flow shop scheduling under machine breakdown

Manufacturing systems in real-world production are generally dynamic and often subject to a wide range of uncertainties. Recently, research on production scheduling under uncertainty has attracted substantial attention. Although some methods have been developed to address this problem, scheduling under uncertainty remains inherently difficult to solve by any single approach. This article considers makespan optimisation of a flexible flow shop (FFS) scheduling problem under machine breakdown. It proposes a novel decomposition-based approach to decompose an FFS scheduling problem into several cluster scheduling problems which can be solved more easily by different approaches. A neighbouring K-means clustering algorithm is developed to first group the machines of an FFS into an appropriate number of machine clusters, based on a proposed machine allocation algorithm and weighted cluster validity indices. Two optimal back propagation networks, corresponding to the scenarios of simultaneous and non-simultaneous job arrivals, are then selectively adopted to assign either the shortest processing time (SPT) or the genetic algorithm (GA) to each machine cluster to solve cluster scheduling problems. If two neighbouring machine clusters are allocated with the same approach, they are subsequently merged. After machine grouping and approach assignment, an overall schedule is generated by integrating the solutions to the sub-problems. Computation results reveal that the proposed approach is superior to SPT and GA alone for FFS scheduling under machine breakdown.     

Low-voltage superjunction technology

The scalability of superjunction and superfield power MOSFET technologies to breakdown voltage lower than 250 V is investigated. The influence of device geometry and process architecture on the switching figures-of-merit of these relatively new classes of power switches with a breakdown voltage rating of 80 V is presented. The current flow and field distributions inside these devices are described. Using Gauss's law, the field-induced compensation of the doping density in the drift region during the blocking state of both superjunction and superfield MOSFETs is calculated from the knowledge of the lateral field distributions. It is shown that the problem associated with imperfect charge compensation at the edge of the die for a superfield effect power MOSFET structure can be avoided by using an unconventional racetrack layout design.     

Genetic algorithm for job-shop scheduling with machine unavailability and breakdowns

The job-shop scheduling problem (JSSP) is considered to be one of the most complex combinatorial optimisation problems. In our previous attempt, we hybridised a Genetic Algorithm (GA) with a local search technique to solve JSSPs. In this research, we propose an improved local search technique, Shifted Gap-Reduction (SGR), which improves the performance of GAs when solving relatively difficult test problems. We also modify the new algorithm for JSSPs with machine unavailability and breakdowns. We consider two scenarios of machine unavailability. First, where the unavailability information is available in advance (predictive) and, secondly, where the information is known after a real breakdown (reactive). We show that the revised schedule is mostly able to recover if the interruptions occur during the early stages of the schedules.