Novel method of measuring tappet rotation and the effect of lubricant rheology

One of the main drivers for developing lubricant technology is engine durability. Researchers and scientists are using new technologies, materials and advanced lubricant formulations to reduce overall engine friction and wear. One of the main engine tribological components is the valve train. This is one of the most challenging components to lubricate effectively because of the higher contact loadings and accounts for 10–20% of the total engine friction loss. The two main factors affecting the performance of engine valve trains are wear and friction, and a wide range of mechanical configurations are used to improve these. For example, direct-acting overhead camshaft valve train configurations use a rotating tappet design. Normally, the tappet is slightly offset from the cams and the cam is slightly conical to match the domed tappet to facilitate tappet rotation for even wear and to reduce slippage. In this paper, a novel innovative technique has been described to monitor tappet rotation in a real production engine having a direct overhead cam–tappet arrangement. The monitoring technique was applied to a VW Tdi engine head, and tests were carried out under different operating conditions. Lubricant compositions, oil temperature, pressure and camshaft speeds on tappet rotation were measured and all are shown to have an effect. The balance of forces between the cam–tappet and tappet-bore was found to be interlinked and the design of the hydraulic lash adjuster had a significant effect.This unique tappet rotation monitoring system can be used on most of the direct overhead camshaft engines, with minor engine modifications, to measure lubricant and hardware effects under both motored and fired conditions.     

DLC涂层改善气门挺柱摩擦学性能的试验研究

为探求DLC涂层对气门挺柱摩擦学性能的影响,制备了三种不同表面处理的气门挺柱,搭建了配气机构试验台架,对比分析了不同顶面处理方法的气门挺柱在不同转速和缸盖温度下的摩擦功耗;测试了试验前后气门挺柱和凸轮的表面形态,研究了DLC涂层表面特性及其耐磨损特性。试验结果表明,DLC涂层能够减小气门挺柱表面粗糙度,含Si的DLC涂层表面粗糙度极小;气门挺柱与凸轮之间的摩擦力矩随着凸轮轴转速上升逐渐减小,随着缸盖温度上升逐渐增大;相对于传统碳氮共渗气门挺柱,DLC涂层能有效减小摩擦损失,含Si的DLC涂层能减小高达20%的摩擦损失;无涂层气门挺柱和不含Si的DLC涂层气门挺柱的耐磨性较差,含Si的DLC涂层具有极好的耐磨性。     

Valvetrain Friction Reduction through Thin Film Coatings and Polishing

In a direct-acting mechanical bucket tappet–type valvetrain, the cam and tappet contact is responsible for about 85% of the total valvetrain frictional losses. Because this contact operates primarily in a mixed lubrication regime, it offers an opportunity for friction reduction through surface engineering. The friction reduction potential of thin Mn-phosphate coating, diamond-like carbon coating, and polishing on the bucket surface was explored using a motored valvetrain rig equipped with 3.5L V6 engine head. The durability of tappets and cam lobes was also evaluated using a different motored valvetrain rig consisting of a single lobe and a single tappet. The polished buckets demonstrated substantial friction benefit over current production buckets at all speeds investigated. The diamond-like carbon coated buckets did not show any additional friction reduction benefit. The wear data demonstrated much less wear with polished buckets and also for cam lobes when in contact with polished buckets compared to current production buckets and cam lobes. The composition of antiwear surface films on polished buckets was found to be similar to that on current production buckets.     

Valvetrain Friction and Wear Performance of Polyalkylene Glycol Engine Oils

The application of polyalkylene glycol (PAG) as a base stock for engine oil formulation has been explored for substantial fuel economy gains over traditional formulations with mineral oils. Various PAG chemistries were explored by varying the feedstock material. All but one formulation have the same additive package. The friction performance of these oils was evaluated in a motored valvetrain rig with current production engine hardware in the temperature range 40–100°C and in the speed range 300–2,500 rpm. PAG formulations showed up to 48% friction reduction over GF-5 SAE 5W-20 oil depending on temperature, speed, and oil chemistry. The wear protection capability was evaluated using a radiotracer technique on another motored valvetrain rig where only one cam lobe rotated against a bucket tappet. The wear trend of some PAG oils was equal to or better than that of GF-5 SAE 5W-20 oil, whereas others showed high initial wear. The wear rate of the PAG oils was not significantly different from that of GF-5 oil. The bucket tappet surfaces were analyzed using scanning electron microscopy, auger electron spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectroscopy to characterize the tribofilm formed and to help explain the friction and wear performance.     

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.     

Cam and Tappet Lubrication. IV–Radioactive Study of Sulfur in the EP Film

A radioactive tracer, sulfur-35, synthesized into zinc dialkyl dithiophosphate molecules, was used to study the EP film formed on cast iron cams and tappets run in motor oils containing this additive. The sulfur content of static films increased with immersion time and temperature, and the presence of phosphate-coated metal surfaces. The bound sulfur of films formed during dynamic tests increased with running time, load, and with the use of phosphate-coated surfaces. These conditions also influenced the ratio of Zn:P:S contained in both static and dynamic films. Zinc, and particularly phosphorus, in the films increased more rapidly than the sulfur with increased temperature and/or pressure. The dynamic films are not easily worn off by running in nonadditive oil. The mechanism of action of zinc dithiophosphates appears to be related to chemical reactions of additive decomposition products with the metal surfaces to form tightly-bound solid films which reduce damage under extreme pressure conditions. Radioactive counting and X-ray spectroscopy were used to obtain the amount of sulfur and zinc on tappets. Densitometer traces of the autoradiographs were utilized to determine the distribution of the sulfur on cam and tappet surfaces.     

挺柱热挤压工艺及其尺寸检测方法

以150系列和396系列大功率高速柴油机挺柱热挤压为研究对象，着重介绍了挺柱热挤压成形工艺特点，热挤压模设计的原则，及其尺寸检测的有效方法。     

柴油机机体气门挺杆孔加工工艺改进

现行柴油机机体挺杆孔加工工艺柔性不足,为此,本文结合生产实际,提出了新的工艺廊,使研制的柴油机机体挺杆孔加工组合机床具有一定的柔性,以适应同一系列不同缸数的同体挺杆孔的加工。     

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。     

The Experimental Study of Laser Microprecision Treatment of I. C. Engine Tappet

The cam-tappet of an I. C. engine is a rubbing pair with high load and severe lubrication condition. In order to raise the anti-scuffing capacity of the cam-tappet, a laser microprecision treatment was adopted to make the topography with artificial regular asperities on the working surface of tappets. It was proved by experiment rising a full-scale engine rig that the tappets treated by laser microprecision had an obvious antiscuffing effect.     

零部件优化对发动机燃油经济性影响的研究

为了降低发动机的机械损失,提高燃油经济性,考虑对挺柱和水泵进行设计优化,从而降低挺柱的摩擦损失和水泵的功耗。利用发动机台架测量整机的机械损失扭矩和万有特性油耗,配合方差分析,研究挺柱和水泵的优化对燃油经济性的影响。结果表明,挺柱和水泵的优化均可提高燃油经济性,其中挺柱影响最显著,而它们的交互作用无影响。     

The antiwear mechanism of zddp's. Part II

The solution breakdown of zddp's to zinc polyphosphates and mixed alkyl sulphides has been discussed. In this paper, their interaction with metal surfaces is pursued using esca. Zinc phosphate is demonstrated to arrive in the surface oxide layer of engine cams and tappets by physical adsorption and FeS is formed via the oxide layer and elemental sulphur generated from alkyl sulphides with Fe₂O₃. It is hypothesized that their presence there as fusible glassy compounds, phosporus as polyphosphate and iron sulphide as a ternary eutectic with iron oxide, provides the antiwear function of zddp     

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.     

发动机凸轮轴异常磨损分析

某型发动机在运行早期出现异响,经拆解发现凸轮轴存在异常磨损,从凸轮与挺柱的材质、硬度、凸轮轴型线等方面进行分析,得出凸轮轴与挺柱的偏心量设计不合理是凸轮轴磨损的主要原因.通过优化凸轮轴型线,变更挺柱设计,显著改善了凸轮轴的磨损情况.     

Cam and Tappet Lubrication III — Radioactive Study of Phosphorus in the EP Film

A radioactive tracer, phosphorus-32 synthesized into zinc dialkyl dithiophosphate molecules, was used to study the EP films formed by this motor oil additive on cast iron cams and tappets. The tightly bound films, which contain phosphorus and zinc, formed rapidly and then approached steady-state values in static and dynamic tests. The amount of film increased with oil temperature (200 to 300F) and with available surface area. Dynamic test conditions greatly increased the amount of film formed, indicating the marked effect of surface temperature, pressure or wear. The film is maintained on parts run in additive oil; moreover, the film was not easily worn off in non-additive oil. The chemical and physical properties of the films appeared to vary with the conditions of film formation. Radioactive counting was used to determine the film on tappets and the thermal stability of the compounded oil. Autoradiographs showed the concentration and distribution of the film on cams and tappets.     

基于转速反馈的正面吊防熄火控制研究

针对正面吊运机在重载状态时,发动机容易过载而熄火的问题,分析了发动机与液压系统的功率匹配问题,通过研究发动机的工作特性,提出了一种基于转速反馈的防熄火控制方法,采用增量PD控制算法控制发动机的失速率保持在一个适当的水平,既保证了发动机不熄火,又尽量利用了发动机的转矩能力,并且保持发动机转速的变化平稳,通过在合力RS4532型正面吊运机上进行实际实验,验证了该方法的有效性。     

Network analysis of an engine lubrication system

A computer program for the analysis of engine lubrication systems has been developed. A case study of a four-cylinder gasoline engine is illustrated. This paper gives the mathematical models for oil flow through a hydraulic tappet as well as those of an oil jet and plain journal bearings. The flow from an oil pump and the flow resistance through an oil filter is considered at various temperatures. In the analysis, various design guidelines are applied. The distribution of flow and pressure of an engine lubrication system is calculated, and the pressure data compared with the experimental data at a few points in the engine lubrication system. This method is helpful to design an engine lubrication system efficiently.     

A review of scuffing models

The mechanism of wear known as scuffing has been a research topic of great interest for many years. However, the question of how scuffing is initiated and the factors that contribute to its occurrence are still poorly understood. In general, it can be said that scuffing manifests itself as the sudden failure of lubricating films in mechanical equipment operating under extreme conditions of load and/or speed. Components such as cams, tappets, gears and piston rings are all prone to scuffing failure. Understanding the mechanisms that initiate failure would enable the development of criteria for scuffing prediction. This paper reviews the numerous scuffing models and theories that exist today and, in doing so, defines the important factors involved in scuffing initiation. Emphasis is given to existing theoretical scuffing models which have been correlated by a wealth of research data obtained from experimental test rigs.     

DCVVT发动机外特性转矩下凹问题的研究

DCVVT发动机耐久性试验中,在转速1 500~2 500 r/min时外特性转矩存在明显下凹,而标定试验过程中外特性转矩无此下凹问题。采用一维仿真和试验验证相结合的方法,证明排气系统管路的不一致造成此发动机转矩的下凹。进一步研究发现,当DCVVT发动机进排气门重叠角大时,发动机的外特性对排气系统前级催化反应器与后级催化反应器之间管路长度的变化很敏感,可采用缩短此段管路长度的方法来避免发动机耐久试验外特性在转速1 500~2 500 r/min时的转矩下凹。     

发动机配气机构系统的动力学建模及仿真分析

针对发动机配气机构系统,在ADAMS／Engine软件中建立了其虚拟模型,在此基础上,对该机构进行了仿真分析,得到了气门的升程、速度、加速度和摇臂与挺柱的接触力等特性曲线,为配气机构动态性能的评价和优化提出了理论依据,从而为虚拟样机技术在新产品开发中的应用提供了有效方法。