某高速柴油机配气机构动力学仿真分析

本文采用AVL EXCITE Timing Drive软件对某高速柴油机新设计的配气机构建立单阀系模型,评价凸轮型线和配气机构各零件的动力学表现。通过气门升程丰满系数,凸轮与挺柱的最大接触应力和润滑效果、气门落座时是否出现反跳、气门弹簧是否出现并圈来评价进、排气凸轮型线设计的合理性,验证此配气机构设计的可靠性。     

四缸汽油机配气机构进气凸轮型线的改进设计

针对某型四缸汽油机配气机构进行进气部分运动学和动力学分析,分析表明配气机构存在进气门跃度值偏大,进气凸轮与挺柱间的最大接触应力过大,气门落座力过大等缺陷。因此,对进气凸轮型线缓冲段和工作段重新设计,缓冲段选用简谐运动规律,工作段选用多项式动力学运动规律,进气凸轮型线工作段的设计参数对凸轮型线的形状和汽油机综合性能有很大的影响,进而以设计参数为变量对工作段进行正交试验设计,利用综合分析法对工作段的参数进行优化匹配,得到了新型凸轮型线。     

基于接触应力及润滑特性分析的配气凸轮基圆半径计算

平底配气凸轮机构凸轮基圆半径的选择将直接影响凸轮机构的结构尺寸、接触应力和润滑性能。利用赫兹应力公式对平底配气凸轮机构接触应力进行分析,利用弹性流体润滑理论对其进行弹性流体动力润滑分析,得到了基圆半径与接触应力和润滑系数间的关系。结果表明：增大凸轮基圆半径可以降低凸轮接触应力,但却不一定能改善凸轮润滑情况;对于给定从动件运动规律的平底配气凸轮机构,利用赫兹应力公式和弹性流体润滑理论同时对基圆半径的取值范围进行约束,才能使配气凸轮同时满足接触应力和润滑要求,从而保证配气机构的可靠性和耐久性。     

基于AVL/TYCON的非对称凸轮型线设计研究

利用配气机构模拟计算软件AVL/TYCON,在国内某具有液压挺柱的四缸汽油机的基础上,采用多项动力加速度函数、分段加速度函数和多项动力一分段加速度函数三种函数方法拟合非对称凸轮型线.将配有液压挺柱的配气机构当量成单质量运动模型,并结合其他参数,应用AVL软件模块建立AVL运动学模型,通过该模型计算出凸轮型线的位移和速度,并分析对比不同凸轮型线的丰满系数、跃度以及凸轮和液压挺住的最大接触应力.最后,建立动力学模型,分析气门和气门座的耐久性.     

基于润滑特性分析的配气凸轮设计

平底从动件配气凸轮在桃尖附近容易出现润滑危险区,磨损较大,需要进行润滑特性分析。研究表明:配气凸轮桃尖附近润滑系数应满足Nr≥0.5或0.15≤Nr≤0.25,改变凸轮桃尖附近加速度值或凸轮基圆半径,配气凸轮机构获得较好的油膜润滑特性。保证凸轮与从动件之间满足润滑特性要求,能够有效降低配气凸轮机构磨损,当0≤Nr≤0.25或Nr≥0.5,可以增大基圆半径以改善润滑情况;当0.25Nr≤0.5,应根据凸轮尺寸和接触应力要求增大或减小基圆半径,以满足润滑要求。     

基于MATLAB汽车发动机配气凸轮的型线设计与接触应力分析

在汽车发动机配气凸轮的型线设计过程中,通过选用合适型线函数,设定预期从动件运动边界条件,推导凸轮接触应力计算公式,进而通过MATLAB编程,可生成预设的从动件升程、速度、加速度和凸轮接触应力曲线。文中所涉及的MATLAB程序以期快速完成凸轮设计和分析凸轮接触应力为目的,应用此方法可显著提高配气凸轮设计的速度和精度,并为凸轮机构的优化提供理论依据。     

船用柴油机凸轮动态摩擦学分析及型线优化设计*

柴油机配气凸轮工作环境较为恶劣,工作过程中配合界面间载荷、速度及曲率半径等工况周期性变化,导致润滑接触条件苛刻,磨损情况恶劣。以某船用柴油机配气凸轮机构典型工况为算例,针对凸轮-挺柱常见的磨损问题,研究凸轮-挺柱动态接触特性;采用余弦-等速段和高次五项式对凸轮型线进行优化设计,并对凸轮-挺柱副动态接触及弹流润滑状态进行数值分析。结果表明:原凸轮磨损的原因是凸轮-挺柱副在运动周期内动态接触应力出现明显波动,最大值超过许用应力值;经型线优化设计后,凸轮-挺柱动态接触应力降到许用值以下,改善了动态接触特性,凸轮型线具有较好的润滑特性,运行过程中可保持较稳定的油膜润滑状态;凸轮转速和接触载荷的改变会直接影响凸轮-挺柱的润滑状态,尤其是随凸轮转速增大,润滑膜厚增大,压力减小,润滑接触状态明显改善。     

基于改进型蚁群算法的内燃机配气凸轮机构型线动力学优化设计

针对内燃机配气机构工作时的振动、冲击和噪声问题,建立内燃机配气凸轮机构型线的动力学数学模型。对蚁群算法在内燃机配气凸轮机构型线参数优化设计进行详细分析,并对蚁群算法存在的容易陷入局部解问题,将蚁群算法和遗传算法进行有效地结合,使得改进后的蚁群算法能够高效率地对内燃机配气凸轮机构型线参数进行优化设计：运用改进型蚁群算法和Matlab语言,对内燃机配气凸轮机构型线数学模型进行仿真优化计算,与原设计相比,仿真结果表明,丰满系数提高,动态最大正加速度在上升段降低,在下降段增加,动态最大负加速度降低,使得系统动态速度和动态加速度趋于平稳,有效地减少了内燃机配气机构的冲击振动,提高了内燃机的动力性能。     

基于摩擦学的顶置凸轮轴式配气机构改进设计

分析了某顶置凸轮轴式配气机构凸轮与摇臂之间的作用力,计算了凸轮与摇臂之间的接触点的综合曲率半径变化和凸轮与摇臂之间的动态局部接触应力;计算了凸轮与摇臂之间的动态润滑油膜厚度;分析了凸轮与摇臂之间润滑油卷入的特点.将凸轮轮廓型线改为非对称的设计,降低了凸轮与摇臂之间接触压力角,改善了润滑状态,解决了凸轮与摇臂之间早期擦伤问题.     

基于MATLAB配气凸轮接触应力计算

配气凸轮表面的接触应力很大时,将引起配气凸轮轮廓表面过早地产生接触疲劳破坏和磨损,致使配气机构的使用寿命缩短,配气性能降低。以赫兹理论为依据,考虑配气凸轮从动件惯性力对接触应力的影响,使用MATLAB软件编写接触应力计算程序,得到不同发动机转速下的接触应力曲线。由接触压力曲线可知:最大的接触应力值出现在配气凸轮桃尖处。仿真结果表明:最低发动机转速(如怠速)时,配气凸轮最危险。可根据怠速时的最大接触应力进行接触强度校核。     

Predictions of cam follower wear in diesel engines

The rate of wear of cam followers in a valve train system is mainly a function of contact stress between the cam and the follower, sliding velocity and hydrodynamic film thickness between the two mating surfaces. The problem of surface fatigue wear becomes severe as the contact between cam and follower exceeds the plasticity limit of material. It finally leads to an increase in valve lash and loss of engine performance. The wear is minimised by reducing the coefficient of friction and by minimizing the compressive stress.In this paper, an attempt has been made to estimate the wear of followers quantitatively. The profile of followers resulting from steady and non-catastropic wear processes is computed by combining a linear wear relation and an elasto-hydrodynamic or boundary lubrication transition model with kinematic analysis. The finite element analysis, AVL TYCON simulation program and classical methodology have been effectively used to predict the follower wear. The model was validated on all types of followers widely varying in size, brake mean effective pressure and speed. The predicted wear profiles exhibit satisfactory agreement with experimental observations. At the end of the paper, a design guideline for designing a cam follower for low wear rate is given.     

N次谐波凸轮-挺柱副的润滑特性分析

将线接触弹流润滑理论应用于发动机配气机构，计算了某N次谐波凸轮-挺柱副润滑的稳态最小膜厚、膜厚比等参数，分析了凸轮．挺柱副稳态润滑在设计转速下随凸轮转角的变化特征，比较和讨论了发动机转速变化对润滑性能的影响。结果表明，凸轮桃尖区多为部分弹流润滑状态和边界润滑，工作段其它部分多为部分弹流、完全弹流和动力润滑状态。曲轴转速提高一般情况下对增加稳态最小膜厚有利，但由此导致的载荷波动量增加对最小膜厚的稳定性不利，从而使表面摩擦和磨损的可能性增加。     

Simulating cam and follower wear in valve train

ABSTRACT

The paper aims to predict the cam and follower wear in direct acting valve train considering the effects of operating conditions. A numerical approach has been developed using frictional and lubrication analysis which is applied in the cam/follower wear study. Loading and motion parameters have been determined from dynamic and kinematic analysis whereas the wear profiles are obtained by linear wear relation. The wear of cam/follower is largely dependent on the lubrication film thickness, normal loading/contact pressure and sliding velocity. At low camshaft speeds, the wear depth of cam/follower pair is higher whereas it decreases at higher speeds due to relatively thicker oil film. It is an original research work and is strongly believed that it would help to further improve the performance of engine valve train and would also provide an opportunity to control the operating conditions promoting wear.     

多目标优化设计在配气机构凸轮型线中的应用

分析了发动机配气机构凸轮型线设计要求和型线选择,建立了凸轮型线多目标优化数学模型,基于Matlab软件编制了凸轮型线进行多目标优化设计的程序。给出了计算实例,实例表明通过优化改善了挺柱运动的平滑性,提高了配气机构的性能。     

Investigation of dynamic characteristics of a valve train system

A valve train dynamics model of internal combustion engine has been developed using the kineto-elastodynamics method. The dynamics behavior for flexible components such as the valve springs in the valve train system was described by the wave equation. The contact force at the cam/tappet interface was estimated by the elasto-hydrodynamic lubrication theory of finite line conjunction. Component submodels were integrated into the whole valve train model by coupling the corresponding contact and friction forces, and solved simultaneously considering transient effect of lubrication, as well as the torsional and bending vibrations of camshaft. Experimental validation was performed on a motored test rig. The predicted results agree well with experiments at difference camshaft speeds. The effects of the bending deflection and torsional vibration of camshaft on performance of the valve train system were also studied.     

A computer-aided method for optimum design of plate cam-size avoiding undercutting and separation phenomena—II: Design nomogramsEine rechnergestützte methode zur konstruktion optimaler kurvengetriebe ohne unterschnitt und anheben der rolle. Teil 2: Konstruktionsnomogramme

This study presents design nomograms which make it easy for the cam designer to estimate the limiting value of the investigated parameter which can be applied to a plate cam follower system, as long as the maximum contact stress between the cam and follower during both rise and return strokes of cam revolution can be determined. The undesirable phenomena of the undercutting of cam profile and the separation between the cam and the follower are taken into consideration. Moreover, these design nomograms give correlations between the investigated parameters and the optimum plate cam size and also are used to study the influence of an investigated parameter on this size. The optimum plate cam size is the combination of cam base circle radius and the amount of cam follower offset, and satisfies the suggested design procedure which is based on taking the contact stress as a design criterion. The investigated parameters are dynamic, kinematic, geometric and material. A brief discussion on using the suggested design procedure to design the size of plate cam is described. For a numerical example, the presented design nomograms are for reciprocating cam-roller-follower which operated by parabolic plate cam.     

An analysis of valve train behavior considering stiffness effects

To maintain the specific volumetric efficiency of a heavy-duty diesel engine, an understanding of the behavior of each part of the valve train system is very important. The stiffness of the valve train system has a strong influence on the behavior of the valve train than valve clearance, heat-resistance, or the durability of parts. In this study, a geometrical cam design profile using a finite element model of the valve train system is suggested. The results of the valve behavior according to the change in stiffness is analyzed for further tuning of the valve train system.