Crirical physical conditions in the lubrication of automotive valve train systems

Pivoted follower valve train systems are now widely used in modern high-speed automotive engines, and because of their proneness to wear they feature prominently in lubricant specification test requirements. Critical conditions for wear in these systems have been identified by the application of a new model for steady, non-catastrophic,wear processes to the kinematic analysis of the cam/follower contact cycle. It is shown that using this technique, the positions of maximum wear and the reasons for the observed wear severity of pivoted follower systems can be more accurately identified than previously.     

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.     

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.     

平底直动从动件凸轮机构磨损失效分析及磨损量计算

凸轮轴和挺杆体是发动机的重要零件,它们的状况直接影响着发动机能否正常工作.文中研究了平底直动从动件凸轮机构运动模型和受力情况,并对其磨损失效成因、磨损形式、磨损规律进行了分析;剖析了相对滑动、润滑条件和接触应力对其工作环境的影响机理,建立了磨损计算模型;并提出从凸轮挺杆材料选配、润滑油、运动参数方面降低凸轮机构磨损的相应措施;提高了凸轮机构的工作可靠性,延长了工作寿命.     

平底从动件盘型凸轮机构系统磨损的数值仿真

磨损寿命预测、状态监测及参数优化设计是摩擦副系统的磨损过程中的三大难点。我们基于离散数学理论和计算机技术建立了平底从动件型凸轮机构系统磨损的数值仿真模型,通过引入位置矢量和磨损步长的概念,使连续的磨损过程离散化,实现了对凸轮的磨损寿命的预测,并对从动件的运动规律做了动态跟踪。     

Sliding wear rig

As a preliminary to studies on cam and follower systems, a rotating cylinder on reciprocating flat wear rig has been developed. This has turned out to possess a number of useful characteristics not available in more conventional rigs. The rig has been particularly useful in that it has produced wear areas large enough for detailed comparison of a range of quantitative surface analysis methods. Esca, sem/empa, sem/edax have been compared for the quantification of antiwear surface elements.     

采用实际模型对自动齿轮箱凸轮作动器的效率和磨损的研究

本文研究自动齿轮箱凸轮作动器的效率和磨损,着重于接触动力学。采用罚函数方法仿真凸轮和从动杆间接触,该模型基于有限元与连续弹性基础梁理论近似。采用Hertz理论考虑凸轮和从动杆间相对运动时主要曲率的变化计算基础模量。为比较接触力和不同凸轮轮廓的磨损,该模型仿真概括了整个档位。     

一种新型凸轮机构—凹圆弧底从动件盘形凸轮机构的设计（一）

本文根据赫兹应力理论，提出一种凹圆弧底从动件的盘形凸轮机构。这种机构能够显著提高凸轮高副的接触强度，降低磨损，延长寿命，较之传统的凸轮机构更加适应高速重载的要求。本文就这种新型凸轮机构的理论基础与凸轮轮廓曲线的设计步骤进行了详细论述。     

用最优控制理论设计高速凸轮-从动杆系统

本文将最优控制理论用于高速凸轮-从动杆系统的设计,对凸轮-从动杆系统存在着众多而又相互矛盾的设计要求,本文提出的性能指标泛函对众多的设计要求都有显著效果,该优化设计法与传统的多项式设计方法相比较,使最大接触力、接触应力以及能量损失分别减小了19%、10%及17%,同时使凸轮-从动杆分离的凸轮工作转速提高6%。在减小压力角、凸轮曲率以及从动杆力等重要性能方面也有显著改善。     

Contact Stress Distribution of a Pear Cam Profile with Roller Follower Mechanism

The problem of this paper is the high contact stress at the point of contact between the cam and the follower.A pear cam and roller follower mechanism were studied and analyzed for different position of the follower and different contact compression load.The objective of this paper is to study the effect of contact compression load on the contact stress distribution of the cam profile at the point of contact.Four different positions of the follower with the cam was considered(0°,90°,180°,and 270°).The theory of circular plate was applied to derive the analytic solution of the contact stress.The numerical simulation had been done using ANSYS Ver.19.2 package to determine the contact stress,while SolidWorks software was used to investigate follower displacement,velocity,and acceleration.Four distinct values of the compression contact load,such as 3.121 N,6.242 N,9.364 N,and 12.485 N,were used in the numerical simulation.In the experiment setup,a photo-elastic technique was carried out in the field of polarized light to exhibit the stress distribution on the cam specimen.The annealed PSM-4 backalate material was used in the experiment setup.The experimental value of contact stress was checked and verified analytically and numerically at the point of contact.The innovation in this paper the use of spring-damper system which reduce the value of contact stress at the point of contact.The contact stress was maximum 2.136 MPa when the follower located at 270° with the cam,while the contact stress was minimum 1.802 MPa when the follower located at 180°at compression load 12.485 N.     

Synthesis of cam-follower systems with rolling contactSynthese der kurvengetriebe mit rollberührung

The present work deals with the synthesis of cam follower systems with rolling contact during the rise period of a dwell-rise-dwell return cam. It has been found that the total lift of the follower can not be achieved solely by rolling contact, therefore sliding is permitted for a fraction of the lift. On the basis of minimum work-loss, the respective percentages of contribution by pure rolling contact and rolling cum sliding action have been worked out.     

多圆弧凸轮接触点位置的计算机辅助求解

提出了一种简单有效的多圆弧凸轮机构瞬时接触点位置的计算机辅助求解方法,它通过分析凸轮与从动件的瞬时接触公法线与圆弧区域界线之间的相对关系来判断任一瞬时凸轮与从动件的接触点的位置、接触点处的曲率半径和曲率中心的位置,据此,可对凸轮机构进行高副低代和运动分析。该方法对于直动、摆动、尖顶、滚子、平底从动件凸轮机构均适用。应用被建议的方法对含平底摆动从动件圆弧凸轮的多功能家用缝纫机送料机构进行了运动分析及动态仿真,验证了该方法的有效性。     

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.     

A study of the measurement of surface temperature at a cam/tappet contact

Cam/tappet wear is one of the most difficult reliability and durability problems to predict during the development of a prototype engine valve‐train system. In the present study, the cam/tappet surface temperature was measured and calculated to determine the effect of surface temperature on the lubricating conditions at a cam/tappet contact. The measurement method, sometimes called the dynamic thermocouple technique, was based on the Seebeck effect: by using different materials for the cam and tappet, the cam/tappet contact point becomes the hot junction of a ‘thermocouple’. The cam/tappet contact surface temperature can therefore be measured continuously. The measured temperature results show good agreement with predictions. Temperature spikes, however, were not found in the test using new oil, but were shown by the theoretical model. Such results indicate that the cam/tappet interface operates in effective lubricating conditions, even when the oil temperature is relatively high. Further research with degraded oil supplied at high temperature is needed for a thorough understanding of abnormal cam wear.     

设计盘形凸轮廓线的相对速度法

提出了一种利用凸轮与从动件的相对速度设计盘形凸轮轮廓的新方法，该方法基于从动件和支承绕凸轮轴线反转的原理，利用从动件上的接触线或者滚子轴线相对固定凸轮的速度和凸轮与从动件的几何关系设计盘 形凸轮轮廓，应用该方法导出了四种不同类型凸轮机构的凸轮廓线的解析表达式，并给出了对应的设计实例。     

Scuffing detection of TU3 cam–follower contacts by electrostatic charge condition monitoring

The increasing costs associated with lubricant development and qualification has driven the need for condition monitoring techniques to be deployed on test engines to maximise information gained from expensive testing programmes. This paper discusses the results from a motorised TU3 engine with electrostatic sensors focused on the cams. System characterisation tests and an oil starvation test were used to decouple charge mechanisms associated with a lubricated wear test, accelerated through the use of carbon black. Cross-correlation of various charge signal processing techniques, scanning electron microscopy and profilometry revealed that tribocharging dominated during running-in/mild wear and contact potential difference (CPD) dominated during the progression of severe adhesive wear. Tribocharging (the charge generated by a low conductivity fluid) has been shown to be affected by oil temperature, cam rotation speed and the presence of charged species within the lubricant. Contact potential differences was principally generated by the work function difference between oxidised and nascent regions associated with adhesive wear on the cam surface. Electrostatic monitoring which is sensitive to lubricant chemistry and wear, and can be implemented in an industry standard engine, has great potential for the lubricant industry.     

Local order in surface ZDDP reaction films generated on engine parts,using EXAFS and related techniques

The study of reaction films generated in a mild wear lubricated process remains a topic of interest. We present in this paper the latest results obtained by the structural analysis of reaction films directly on friction surfaces. An experimental engine setup is used, in which a cam and follower system is externally driven without combustion. The system is lubricated with a base oil containing ZDDP (zinc dialkyl-dithiophosphate). After the wear test, the engine parts are analysed by the EXAFS technique (Extended X-Ray Absorption Fine Structure) in the Total Electron Yield configuration. It is found that the build-up of the film greatly depends on the formulation of the lubricant, and on the test conditions. In the film formed with ZDDP, the initial Zn-S bonding changed to ZN-O in a completely amorphous arrangement. The nature of the wear debris is found to be very similar to the surface of the reaction film. These results are discussed in terms of microscopic wear mechanisms.     

对心滚子移动从动件盘形凸轮机构的接触应力

当工作载荷较大时,凸轮表面和从动件端部的接触疲劳破坏就成为凸轮机构失效的主要形式之一。但在有关凸轮的教科书中,对接触应力的计算过程论述较少。本文详细分析了对心滚子移动从动件盘形凸轮机构接触应力的计算方法,并给出具体计算例题。     

基于ADAMS的共轭凸轮机构仿真分析

本文以凸轮摆式剪切机中的凸轮剪切机构为研究对象,对摆动从动件共轭凸轮机构进行理论分析,在3维CAD 软件Solidworks中建立凸轮机构模型。以ADAMS的碰撞仿真理论为基础,对机构进行动力学仿真分析,得出凸轮与摆杆之间接触力、凸轮主轴所受力以及凸轮与摆杆之间间隙随凸轮转动的变化规律曲线,并对凸轮与摆杆之间的共轭情况进行了分析。本文对摆动从动件共轭凸轮机构的合理设计和结构参数的优化设计具有一定的参考价值。     

共轭凸轮打纬机构运动精度分析

为了解决国产织机可靠性、稳定性较差,织机速度、运动精度有待进一步提高等问题,借鉴摆动凸轮机构误差分析方法,将凸轮机构反转原理、有效长度理论、转换机构法等多种误差分析技术应用到织机运动精度分析中。开展了剑杆织机共轭凸轮打纬机构在考虑基本尺寸误差、运动副间隙误差及凸轮副磨损误差3种情况下的打纬摇轴摆角误差计算方法的研究,建立了各摆角误差与凸轮转角之间的关系,运用Maple数值分析计算软件对打纬机构的运动精度进行了数学建模及分析计算。研究结果表明,在所考虑的3种主要误差中,共轭凸轮打纬机构的运动精度受凸轮副磨损误差的影响最大,应采取措施控制凸轮副磨损误差。并且该研究对无梭织机的改造和高速剑杆织机的设计应用具有理论指导作用和实用价值。