Coupling of a piston transmission

A gear system with a piston transmission is considered. A formula is derived for the working-section length in the coupling line of a piston transmission with an evolvent lateral tooth surface.     

斜盘式轴向柱塞泵最佳柱塞数确定方法

给出了斜盘式轴向柱塞泵结构及性能的主要影响因素,分析了柱塞数与各因素之间的关联性。运用综合因素评价法,对各因素进行综合性加权比较,得出了柱塞数选取最佳方案。运用该方法确定了K3V型双联轴向柱塞泵设计中的最佳柱塞数(最佳柱塞数为9)。     

Characteristics of pressure and force considering friction in a closed cylinder with a holed piston

A mathematical model for a closed cylinder with a holed piston was established to investigate the operational characteristics of a gas spring. An ideal gas working fluid and an adiabatic process were assumed in the model. Simulation and experimental results for a typical design and operational condition showed good agreement. The model was then used to investigate the effects of the orifice diameter, the filling pressure, and the velocity of the piston on the applied force and operating pressures of two chambers in the gas spring. The results showed that the orifice diameter and the piston velocity had significant effects on the pressure difference between the two chambers. A 0.05-mm reduction in the orifice diameter led to an approximately two-fold increase in the pressure difference. A 10% increase in the piston velocity resulted in an approximately 25% increase in the pressure difference. The orifice diameter and the piston velocity had a greater effect on the chamber with lower pressure than on the chamber with higher pressure. The force applied to the piston also varied with the piston velocity, the orifice diameter, and the filling pressure due to irreversibilities including the throttling process through the orifice and friction between the wall and the piston. The present model and results are expected to supply useful information about a new gas spring design.     

Dynamic analysis of a reciprocating compression mechanism considering hydrodynamic forces

In this paper, a dynamic analysis of the reciprocating compression mechanism of a small refrigeration compressor is performed. In the problem formulation of the mechanism dynamics, the viscous frictional force between the piston and the cylinder wall is considered in order to determine the coupled dynamic behaviors of the piston and the crankshaft. Simultaneous solutions are obtained for the equations of motion of the reciprocating mechanism and the time-dependent Reynolds equations for the lubricating film between the piston and the cylinder wall and for the oil films on the journal bearings. The hydrodynamic forces of the journal bearings are calculated by using a finite bearing model along with the Gümbel boundary condition. A Newton-Raphson procedure is employed in solving the nonlinear equations for the piston and crankshaft. The developed computer program can be used to calculate the complete trajectories of the piston and the crankshaft as functions of the crank angle under compressor-running conditions. The results explored the effects of the radial clearance of the piston, oil viscosity, and mass and mass moment of inertia of the piston and connecting rod on the stability of the compression mechanism.     

液压自由活塞发动机动态特性的仿真研究

液压自由活塞发动机(hydrau lic free p iston engine,以下简称HFPE)是将内燃机和液压泵集成为一体,以液体为工作介质实现动力非刚性传输的一种特种发动机。在左、右动力腔的交替驱动下,HFPE的活塞组件在腔体中作往复直线运动,同时泵出液压油驱动负载工作。与曲轴式发动机不同,由于不受曲柄连杆机构的约束,HFPE活塞组件的运动规律完全取决于其本身的质量及所受到的作用力。本文通过建立所研制的HFPE样机各子系统的数学模型,重点研究了HFPE样机的动态特性,以期为系统的结构及控制系统提供理论依据。     

Friction model of a marine diesel engine piston assembly

In modern marine diesel engines, power output and in-cylinder firing pressures are constantly increasing, leading to higher friction in engine components and especially in the piston assembly. A good understanding of the friction contributions of the various engine components is needed, if mechanical efficiency is to be improved. A friction model for the engine piston assembly has been developed and is presented in this paper. The model, based on lubrication theory, considers the detailed engine geometry and the complete lubricant action, and thus can be applied to a wide range of engines. In detail, the analysis takes into account the friction components of compression rings, oil control rings, piston skirt and gudgeon pin of the engine piston assembly. The model was applied to a four-stroke (medium speed) marine diesel engine and the effect of engine speed and load on friction was examined and compared with results from other semi-empirical models. The engine friction was predicted at constant rotational speed (generator operation) and variable rotational speed (propulsion operation).     

Geometric equation and machining method for the sidewall of a piston

Engine pistons are generally cut with a copy machine or a CNC machine. In recent years, CNC machining has become more popular due to the necessity for increased productivity and accuracy in piston machining. CL data are essential for CNC machining, and such data are usually generated from a 3D CAD model. When using a 3D CAD model, the intersection curves between the surfaces and the cross-sectional plane must be calculated, which is both time-consuming and imprecise. In this paper, a geometric equation for the sidewall of a piston is proposed as a solution to this problem. The geometry consists of an ellipse, recesses, eccentricities, and an offset. The equation for the sidewall of a piston is expressed in terms of the distance from the center. This equation makes it possible to calculate CL data very quickly, and facilitates the compensation of tracking error. A specialized four-axis CNC lathe, suitable for machining the sidewall of a piston, is also introduced. The proposed method has been tested by actual turning using this four-axis lathe. The results demonstrate the practicality of the method in the manufacturing of pistons.     

Friction characteristics of piston rings in a reciprocating engine

The performance of a reciprocating engine can be improved by reducing the friction between piston rings and cylinder liner, which significantly contributes to the mechanical friction losses of an engine. The friction force of a piston ring pack is calculated, based on hydrodynamic lubrication theory, for the piston rings. Calculations were carried out for three sets of conditions. Oil starvation is taken into consideration in the calculation of oil-film behaviour for a ring pack. The friction characteristics of piston rings are evaluated using the frictional mean effective pressure. The friction force of a piston assembly is measured experimentally by an improved floating liner method. The effects of lubricant viscosity and engine speed on friction characteristics are investigated by both calculation and experiment.     

新型摩擦磨损试验台设想

随着我国经济的发展,产业结构调整力度的逐步推进,活塞行业的产业集中度将进一步集中,据有关统计显示,2007年车用发动机活塞总的市场量达到了8000万只,而随着重工业技术水平的提高,活塞产品已向更广阔的领域发展。改善活塞产品的可靠性已经成为重要研究课题,而摩擦磨损试验台正是从事此研究不可或缺的重要工具。     

Experimental study of wear interaction between piston ring and piston groove in a radial piston hydraulic motor

The wear interaction between piston ring and piston groove in a radial piston hydraulic motor was studied in regard to mass loss and changes in form and surface roughness. A specially developed test rig that simulates the tilting movements of pistons at the end of strokes was used in the test. The results show that wear on the piston ring groove can be up to 10 times greater than the wear on the piston ring. For both interacting surfaces, the dominant wear mechanism was mild wear. The results from a factorial design show that the form of the piston groove significantly influences the amount of wear.     

叶片铰接滚动转子压缩机结构特点及工作原理

提出了一种叶片铰接滚动转子压缩机结构型式，并通过与传统结构型式的滚动转子压缩机进行对比，分析了这种压缩机的结构特点，随后阐述了其工作原理，该结构压缩机样机经性能测试，结果基本令人满意。     

新型摇摆活塞式无油润滑空气压缩机的研究

提出一种新型摇摆活塞式无油润滑空气压缩机,利用活塞摇摆运动时与气缸形成的侧隙构成进气通道,并利用曲轴箱作为压缩机的进气消声室。新机型摒弃了易损件进气簧片阀,拓展了进气消声器容积,与传统摇摆活塞机型相比无故障工作时数提高约119／6、噪声降低约5～6dB（A）。研究表明,气缸向压缩行程一侧适当偏置,同时辅以较大数值的曲柄连杆比λ,可以实现活塞侧隙进气,并能确保压缩行程时密封环对气缸的密封性,另外还可减小压缩机的体积;但是,为了缓解活塞对气缸的敲击,必须设置缓冲装置,而且需要强化连杆的散热和隔热,以减小连杆轴承的温升。     

Piston Assembly Design for Improved Thermal-Tribological Performance

The tribological system in the piston assembly of an internal combustion engine includes contacts at interfaces of piston/piston ring/cylinder liner, piston skirt/cylinder wall, and piston/piston pin/ connecting rod. The thermal and tribological properties of the piston, piston rings, and cylinder wall are critical to the life and quality of the engine. Severe wear and scuffing failure, especially at the ring/ring groove and ring/liner interfaces, may present a major problem if the piston temperature is too high. Temperature considerations for the piston often limit the effort to increase the engine power.

A new engine piston incorporating the heat pipe cooling technology has been developed for reducing the piston temperature, especially in the ring land and along the piston wall. The current work aims at investigating the effect of reciprocating heat pipes on heat conduction in the piston, and thus the tribological behavior of the piston assembly. Due to the high thermal conductance of the reciprocating heat pipe, a considerably large amount of combustion heat, which is conventionally conducted through the piston wall, is transferred through heat pipes. This new design will result in a lower temperature on the piston wall and a reasonably low temperature distribution in the piston.     

一种新型伺服直线泵的设计与实验

多电技术成为了飞机未来发展的一大趋势,是当下研究的热点,功率电传电静液作动系统是其核心技术之一。目前已有的或是正在研发的电静液作动器,主要采用旋转伺服电机驱动轴向柱塞泵的架构作为核心能源。轴向柱塞泵虽结构成熟,但却存在着摩擦磨损限制使用寿命,惯性较大限制响应速度,结构复杂难以余度配置等缺点。针对静液伺服传动设计了一种由电磁式直线振荡电机驱动的直线活塞泵,应用协同配流结构,保留原有的泵结构优势的同时,可突破性的提升伺服传动性能。研究搭建了直线泵的仿真模型,验证了该伺服直线泵的基本功能。     

小型航空汽油发动机活塞的设计与研究

论述了小型航空汽油发动机活塞的工作特点,结合发动机活塞设计实例,论述了活塞材料、结构及型面的设计原则和方法。试验结果表明,通过活塞的改进设计,进一步提高了发动机性能。     

Improvement and uncertainty evaluation of mercury sealed piston prover using laser interferometer

Many NMIs (National Measurement Institute) and calibration laboratories are using a mercury sealed piston prover as calibration system for gas flow meter. But it has problems in deciding measuring volume, traveling time of piston and generating low flow rate below 10 cc/min. In this study, a new structure of a piston prover is designed and its flow measurement uncertainty is evaluated according to ISO/IEC 17025. A laser interferometer, instead of optical sensors used in a typical piston prover, is employed to measure testing time and moving distance of the piston, accurately. A new material of the piston is used to eliminate contaminated particles from the material of the piston body. Uncertainty is calculated by evaluating various uncertainty factors which have influence on gas flow measurement. The expanded uncertainty of the piston prover is 0.11% at the confidence level of 95%. The uncertainty evaluation procedure of this study would be useful in flow measurement uncertainty determination of other types of gas flow measurement systems.     

Investigation of heat transfer in an oil cooled piston with and without ceramic insulation on crown face

A numerical method is presented for calculating the temperature fields in a semi-adiabatic diesel engine piston having a cooling oil canal. The crown face of the piston is coated by a 2 mm thick oxide based ceramic insulating material. The non-ideal thermal contacts between the piston circumference and cylinder wall are also considered. A detailed analysis has been given for estimating the boundary conditions of the cylinder-piston assembly of an internal combustion engine. The isothermic distribution in the piston body and the heat flow rate through the different cooling media at four different engine loads have been depicted both for the cases with and without insulation coating. The results indicate a reduction (12–30%) in heat loss through the piston by use of an insulation coating at the piston crown face, assuming that both the heat transfer process from and the temperature of the combustion products remain unchanged.     

某高功率柴油机活塞失效分析及解决方案

针对某高功率柴油发动机铸造铝合金活塞在冷热冲击台架试验后出现顶部开裂现象,综合了活塞及对手件尺寸检测、涡流探伤检测、金相检测及电镜检测的结果,经分析判定为铸造工艺中铝合金氧化皮夹杂是此次活塞出现开裂失效的根本原因.根据分析结果,针对活塞开裂情况提出了对手件设计方案及活塞铸造工艺优化方案并对优化后的活塞进行了三轮冷热冲击...     

液压自由活塞发动机自激振动的控制

以单活塞液压自由活塞发动机活塞运动控制为目标,研究相应的控制方案。基于单活塞液压自由活塞发动机活塞运动系统的理论分析,同时利用样机建立试验测试平台,对活塞运动控制的理论基础、控制回路和控制方法进行研究。通过控制压缩能量的释放时刻可以实现对活塞运动频率的控制。设计出一种新的先导式控制回路及其自由活塞位置反馈调制控制方法。回路实现了对阀组通流能力的充分利用和活塞极限位置的控制。回路循环能量损失的主要来源是节流和泄漏。单活塞液压自由活塞发动机稳定运行充分条件是实现膨胀过程的完整性。     

基于新型复合式单气环与传统活塞环气密性的静态实验研究

介绍了新型活塞环这一新的活塞环密封技术,并通过其来改善活塞环漏气问题。通过实验对比新型活塞环与传统活塞环的气密性,引入漏气通道的当量半径概念,分析对比两种活塞环的气密性优劣,得到新型活塞环的当量半径是传统活塞环的0.86倍,在低压段,传统活塞环漏气量比新型活塞环大3.5×10-10kg/s;在高压段,漏气量差为4.926×10-10kg/s,根据拟合曲线可以得出,气缸压力越大,新型活塞气密性就越优于传统活塞环。