发动机电磁气门驱动(EVA)机构的设计及试验

为给电磁气门驱动(Electromagnetic Valve Actuation,EVA)气门软着陆研究提供适用的平台和探索电磁气门驱动小型化设计,研制了一个装在每缸4气门汽油机缸盖上的EVA装置。采用电磁驱动的传统设计方法与CAE相结合,确定了电磁铁结构、尺寸和线圈参数,其中铁芯由E型硅钢片堆叠而成。EVA装置的总体装配关系中主要考虑了铁芯固定、衔铁运动限位、EVA与缸盖联结等。此外在EVA中布置了电磁铁磁链测量线圈、励磁线圈温度测量电阻。报告了EVA设计过程及初步的仿真和试验结果。     

汽车发动机电磁气门驱动设计与试验

为研究电磁气门驱动（Electromagnetic Valve Actuation,EVA）的气门软着陆控制,研制了装在一个每缸四气门汽油机缸盖上的能够驱动一对进、排气门的EVA装置。EVA设计中确定了电磁铁尺寸、材料,在总体装配关系中主要考虑铁芯定位、速度传感器和位移传感器布置、EVA与缸盖联结等。此外,采用试验和仿真方法对进、排气门EVA进行了电磁力和磁链分析。     

电磁气门驱动设计及其电磁铁静吸力特性试验

根据双弹簧、双电磁铁的电磁气门驱动 (Electromagnetic Valve Actuation,EVA)原理 ,设计制作了用于探索性试验研究的 EVA装置及其电磁铁静吸力特性试验系统 ,测量了电磁铁的静吸力特性。试验结果表明 :1)电磁铁的电磁力达到了设计点的要求 ;2 )在 EVA动态试验中应考虑 3个问题 ,即 :在初始化过程后期线圈逐渐减小电流、保持阶段保证电磁力大于弹簧力以及过渡过程后期线圈所通电流随气隙而变化。     

采用磁场分割法进行的发动机电磁气门驱动(EVA)仿真计算

在对发动机电磁气门驱动(E1ectromagnetic Valve Actuation，简称EVA)进行的仿真计算中，采用磁场分割法建立了电磁铁磁路模型，并根据牛顿第二定律和电压平衡原理分别建立了EVA动力学模型和电路模型，编制了相应的计算程序。计算与试验对比基本符合的情况表明，所建模型反映了EVA的基本特征，整套仿真方法可行。     

发动机电磁气门驱动的精确线性化控制

电磁气门驱动(Electromagnetic Valve Actuation,EVA)是一项可变气门技术,具有很大的潜在技术优势。目前EVA还没有得到实用化,主要难点是控制气门软着陆。EVA是一个非线性系统,气门落座速度控制通常采用的方法是在落座平衡点附近将EVA模型进行泰勒展开,然后使用比较成熟的线性方法控制。双电磁气门驱动EVA将采用精确线性化方法变换成一个全局的线性模型,然后使用LQR线性方法进行控制。其结果是:初始化平均落座速度为0.08 m/s,单次过渡过程平均速度为0.05 m/s。分析可能影响控制效果的诸因素,结果表明:双气门控制中进排气门子系统之间基本上没有干扰,选择合适的控制开始时间可以得到理想的落座速度,但系统参数和传感器测试信号的准确性对控制有较大的影响。     

发动机电磁气门驱动过渡过程的闭环控制

以一个发动机电磁气门驱动(EVA)装置为对象,采用试验方法研究EVA过渡过程。根据EVA的过渡过程工作特点,把过渡过程分为远程、近程两段分别予以控制。远程采用PI控制,控制目标是在远程结束时励磁线圈达到某一电流;近程则采用跟踪位移理想曲线的方法,使落座速度降低。通过试验确定了远程阶段的目标电流和PI控制参数、近程阶段的理想位移曲线和控制点数目,使单次上下行过渡过程落座速度分别达到了0．22m/s和0．10 m/s,实现了EVA连续动作且可使EVA动作适应转速变化。     

采用传统闭环方法控制电磁气门驱动的可行性分析

以研究电磁气门驱动（EVA）气门落座软着陆控制为目的,依据EVA装置,建立EVA的数学模型并将其线性化,在此基础上对采用传统闭环控制方法的可行性进行了分析,得出结论：用于仿真的模型与实际情况有差别,难以用于评估控制策略;在小气隙下EVA系统可控性较差,且非常不稳定,采用传统的闭环方法控制电磁气门驱动不具有可行性。     

发动机电磁气门驱动动态特性试验研究

在电磁气门驱动(EVA)研究中，设计制作了EVA动态特性试验装置和测试系统，对所研制的EVA进行了初始化试验和往复运动试验。试验结果表明，所设计的EVA能够按照其工作原理和控制系统的要求运动，但在开环控制的条件下，不可能实现软着陆，因此EVA必须采用闭环控制系统。     

电磁驱动气门机构系统模型

电磁驱动气门机构是汽车电子控制技术的前沿课题之一。本文针对电磁驱动气门机构的特点建立了包括电磁铁及其机械部分的系统模型，考虑到磁性材料的特性，采用通过测量数据来确定模型参数的策略，并利用该模型对自行设计的电磁驱动气门机构进行了仿真计算，得到了驱动电流和气门升程随时间变化的仿真结果，验证了该模型的正确性。     

发动机电磁气门驱动过渡过程闭环控制研究

由于难以采用传统的闭环控制方法控制发动机电磁气门驱动（EVA），在大量开环试验的基础上提出一个EVA过渡过程闭环控制的新方案，该方案由两个部分组成：运动过程控制和落座控制。运动过程控制能实现较小的落座速度，落座控制能保证落座的成功。在研制的EVA上进行的试验表明，采用这种控制方法能够得到小于0．2m／s的落座速度，但EVA连续动作时平均落座速度大于单次动作的落座速度。     

全可变气门机构运动学的仿真分析

分析了BMW的N52发动机可变升程气门机构的机械结构原理,然后对机构进行运动学方程推导,得出气门升程与凸轮转角、偏心轮转角之间的数学关系,编制了发动机全可变气门升程运动学计算程序,可以用来计算全可变气门机构的运动学问题,为以后进行动力学计算作准备。     

Preliminary Evaluation of a Megawatt-Class Low-Speed Axial Flux PMSM With Self-Magnetization Function of the Armature Coils

This paper presents an axial flux permanent magnet synchronous machine (PMSM) with a disk rotor between two stators, which are wound in a tooth-coil technology (a concentrate winding type with subunitary number of slots/pole/phase). This type of winding facilitates the magnetizing inductor function of stator coils. A potential magnetizing system can be envisioned by taking into account that the coil span and the slot pitch are practically identical, the number of tooth-coils and poles are almost the same, and that there are two rotor poles between four tooth-coils (two adjacent tooth-coils on each stator). Thus, a special magnetizing inductor is not required in order to magnetize, pair by pair, the permanent magnet (PM) rotor poles. The number of tooth-coils exceeds the number of rotor poles by one (Ns = 2p + 1). Some aspects of the average performance obtained in both modes of operation-machine and magnetizing inductor-are highlighted by digital simulation. A scale-down demonstrating model also confirmed the feasibility of the magnetizing inductor function of the stator.     

Prospects for magnetization of large PM rotors: conclusions from a development case study

A development feasibility study has been conducted for magnetizing the rotor of a 1.7 MVA, 20-r/min, permanent magnets (PMs) excited synchronous wind turbine generator. Various technical problem areas and their likely influence on the overall design concept, are reviewed. Thus, some particularly important problems are identified: KERI's conventional facilities ensure sufficient energy for magnetizing, pair by pair, of all the PMs of the rotor. A rotor and inductor optimal arrangement for a magnetizing system's configuration is required in order to avoid a wrong, strong magnetization of the neighboring poles. It is also necessary to take into account the mechanical strength of the magnetizing inductor winding to withstand electromagnetic forces. This paper presents the result of the analytical calculation of such a specialized inductor and a PC Spice-based software simulation of the magnetizer circuit; finally, a transient finite element method (FEM) simulation of the inductors connected by the external electric circuit has been done. All three methods confirm the possibility for a successful magnetization, pair by pair, of all rotor poles. Design proposals are detailed and conclusions are relevant for magnetizing large rotors with surface-mounted PMs in general.     

Encapsulation of PV modules using ethylene vinyl acetate copolymer as a pottant: A critical review

The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150^TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed.