当代凸轮轴机械加工工艺探讨

当代凸轮轴机械加工工艺探讨机械部第三设计研究院刘长吉１凸轮轴机械加工工艺凸轮轴是保证发动机配气质量的重要零件，因此对凸轮轴凸轮型线的制造精度要求越来越高，凸轮轮廓的总升程误差０．ｏｌｍｍ；每度升程误差０．００２５ｍｍ；相位误差：从凸轮到凸轮小于或等于...     

单节凸轮轴机械加工优化

从凸轮加工工艺优化设计、M40型五轴联动车铣加工中心和SN320型数控凸轮磨床的程序编制等几方面入手,完成了单节凸轮轴的工艺优化设计。     

关于磨削凸轮轴降低桃形升程误差的技术研究

通过对桃形磨削原理、凸轮轴自身加工特点的分析,结合生产实际,采用新工装和完善工艺的办法,对凸轮轴重点加工项进行技术突破.就凸轮轴升程值超差的相关因素及解决措施从加工手段、加工方法、标准凸轮钳修等方面进行阐述.     

焊接式组合凸轮轴

凸轮轴是内燃机上最重要的,同时也是很费工时的且可靠性最差的零件之一。凸轮轴最薄弱部位是凸轮,而恰恰是要求凸轮能长久保持几何尺寸不变的性能。 这只是一般情况,下面作一下详细说明。 冷硬低合金铸铁铸出的凸轮具有很好的使用性能。但是从工艺角度看,它们太复杂。     

高供油速率凸轮轴精密磨削工艺研究与验证

针对某型号柴油机高供油速率凸轮轴结构与加工精度要求高的特点,对工艺装置进行改进设计,并对工艺参数进行了优化。在多轮次工艺试验验证的基础上,总结形成了高供油速率凸轮轴精密磨削工艺规范,解决了凸轮高精度磨削问题,满足了该柴油机高供油速率凸轮轴的研制要求。     

300型和G300型柴油机喷油凸轮修复

300型和G300型柴油机凸轮轴喷油凸轮运行中,在圆弧R处(图1)常发生擦伤现象,如不及时修复,还将与其作相对运动的复的基础上,对G6300ZD_3型柴油机(功率1103kW,转速600r/min)发电用的喷油凸轮用堆焊办法作了跟踪修复试验。经修复后的一只喷油凸轮运行720小时,才出现表面擦伤现象,与其相配的喷油泵顶杆滚轮未出     

基于NX的凸轮曲线设计及两种凸轮机构参数转换

凸轮机构是一种由凸轮、从动件和机架组成的传动机构,常用于机械设备中,可以获得较复杂的运动规律。在发动机的结构中,凸轮机构是配气系统的重要组成部分,凸轮轮廓曲面的形状及其加工精度直接影响到进、排气的流量变化。本文主要讲述应用NX进行凸轮轮廓曲线的设计及通过运动仿真分析不同凸轮机构参数转换的方法,为凸轮轴车铣复合加工中心及数控凸轮轴磨床凸轮外形加工提供重要技术依据。     

现代汽车发动机制造工艺的发展动向

本文叙述了发动机五大件加工工艺的发展动向：缸体与缸盖正在发展敏捷柔性生产线取代传统柔性生产线;曲轴的主轴颈和连杆颈的粗加工工艺已由车拉（含车一车拉）、内铣、单刀车削（转塔式）及高速外铣取代了过去多刀车削及普通内铣,并提出了怎样合理选用车拉、内铣、单刀车削及高速．外铣工艺;凸轮轴的凸轮磨削已由 ＣＮＣ无靠模磨削工艺取代了过去机械式靠模磨削工艺;凸轮轴（含曲轴）的主轴颈系统磨削工艺正在发展由高速点磨工艺取代传统磨削工艺,同时最近又开发出凸轮轴（含曲轴）的主轴颈系统和凸轮（曲轴的连杆颈）的集成磨削工艺;连杆分离面正在采用涨断工艺取代传统切削工艺。     

高精度凸轮磨削的凸轮升程误差分析

在凸轮磨削加工中 ,影响凸轮升程误差的因素很多 ,介绍了凸轮轴磨削加工工作原理 ,主要阐述了高精度凸轮轴磨削加工中造成凸轮升程误差的原因。指出凸轮的加工比较复杂 ,应细心调整 ,严格按规程操作     

中空装配式凸轮轴扩径联接强度影响因素分析

针对某汽车发动机装配式凸轮轴,对机械扩径联接强度的主要影响因素进行了数值模拟研究,并进行了钢球扩径联接装配及静扭强度试验对比。研究结果表明:对GCr15钢凸轮和35钢轴管可进行机械扩径联接,材料匹配性能良好,完全满足产品联接强度要求;凸轮与轴管的初始装配间隙值、球体过盈量、轴管厚度和球体加载速度等工艺参数对联接区压配力和静力扭转力矩有很大影响;对工艺参数进行合理选择与匹配,可提高静扭强度35%,且高于凸轮轴产品要求的三倍以上,具有很高的联接可靠性。     

Contents in Volume 23,2014

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Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法,这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。