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PurposeA self-adaptive piston is designed for the compressional gas cushion press nanoimprint lithography system. It avoids the lube pollution and high wear of traditional piston.Design/methodology/approachThe self-adaptive piston device consists of symmetrical piston bodies, piston rings and other parts. The two piston bodies are linked by a ball-screw. The locking nut adjusts the distance between two piston bodies to avoid the piston rings from being stuck. The piston rings are placed between two piston bodies.FindingsThe simulation results based on COMSOL indicate that cylinder vibration caused by self-adaptive piston is 15.9 times smaller than the one caused by a traditional piston.Originality/valueThe self-adaptive piston is superior to the traditional piston in decreasing cylinder vibration.

In this work, the influence of internal combustion engine parameters (cylinder-piston clearance, piston head height, the first segment position, gap of the first piston ring and gap of the second piston ring, piston rings’ axial clearance, intake valve debit coefficient) gas leakage from the combustion chamber through the piston rings’ area was investigated. This influence was studied by making an initial forming operation over gas leakage in the analyzed area.

The purpose of this investigation was to experimentally measure the motion of the floating valve plate in an axial piston pump under various operating conditions and to develop a model to determine how the floating valve plate motion affected the lubricating pressures between the valve plate and cylinder block. In order to achieve the objectives, a hydraulic circuit was designed and developed to incorporate and operate a floating valve plate axial piston pump. The hydraulic circuit integrating the axial piston pump (axial piston pump apparatus, APPA) consists of a series of valves, pressure sensors, a charge pump, flow meters, temperature sensors, a heat exchanger, and proximity probes. The floating valve plate axial piston pump housing was modified to incorporate three proximity probes to measure the valve plate position and motion relative to the cylinder block, thus allowing for determination of the film thickness within this contact. The results illustrate that as the pump starts up the valve ...

Inside labyrinth piston compressor, the piston/piston rod system is main moving part. They suffer from very large periodically varying loads caused by gas force and inertia force. This may result in the piston rod’s bending and vibration. Therefore, the piston is always running eccentrically inside cylinder. It is difficult to calculate and predict the piston’s eccentricity accurately by the traditional analytical method. However, an accurate radial clearance between the piston and the cylinder wall must be calculated in the early design of the labyrinth piston compressor. Thus, this article proposes a new numerical method of studying the piston’s dynamic behavior, which is based on flexible body dynamics and finite element method. The method overall considers the piston rod’s characteristics of bending and vibration, effect of the radial clearance between the piston rod and the guide bearing, as well as crosshead and slideway. Through the model, the piston’s radial eccentric path can be better predicted. In addition, this article also introduces a new idea for realizing piston/piston rod system’s centering and utilizing an electromagnetic guiding system instead of traditional mechanical structure. The new centering technology will simplify greatly the inner structure of the compressor by removing the guide bearing. We have designed theoretically the structure of an electromagnetic guiding system and built its control model. Simulation verifies the effectiveness of this method, and good control result is obtained.

The construction of the piston groove seal of a volumetric hybrid energy-converting piston machine is proposed and investigated. A technique of assessing the overall performance of the proposed groove seal is developed and the influence of the basic construction and regime parameters on the overall performance of the seal is estimated.

All rights reserved. Linear compressors with clearance seals are well established for cryocoolers using either a Stirling cycle or pulse tube. However, both piston stroke and piston offset require detection and control in valved compressors. In order to manufacture linear compressor in large scale, then a simple, robust, and cheap control system is required with a minimum of sensors and actuators. This work introduces an approach to sensing the position of the piston using a search coil. The piston stroke is detected by calculating the peak-to-peak flux linkage in relation to the measured drive voltage and current. The piston offset is proportional to an integrated modulus of the back electromotive force (emf) of the search coil. Two PID (proportional-integral-derivative) controllers were developed to control the piston stroke by adjusting the drive voltage and a solenoid valve and bleed flow to control the piston offset. Experimental results validate the proposed compressor control technique.

Gas springs of the television is to control the piston speed when operating under along stroke(200~300 mm, television elevation)is possible. User by this principle is capable of elevation adjustment. First carried out a flow analysis of the piston. A piston speed adjustment technique for precise pipe type cross-section was examined. The piston structure for flow rate control and elevation action is proposed. This study is the development of a gas spring of more than 50 inch television with a large television stand. Hollow piston rod for optimal control(the outer diameter 19.9 mm, the inner diameter 13.9 mm) was injected into the nitrogen gas(0.3 mm/s) in. As a result, the flow rate the pressure drop of the piston rod as the increase was increased without any change of the external force. As a result, control of the displacement via the gas spring is possible. Keywrds : Gas spring, Labyrinth orifice, Piston, Pipe office

The optimization of the valve plate transition region is an important way of reducing the noise emission for an axial piston pump. However, the optimized methods through simulation or experiment are actually trial and error, and they cannot indicate the precise structural parameters of the valve plate transition region. In this study, a new design method for the transition region of valve plate based on the matching of flow area and reduction of transient reverse flow was proposed, and with which a valve plate was designed. Then, the impact of the flow ripple in the discharge line of an axial piston pump and the pressure overshoot and undershoot in the piston chamber on hydraulic and structural noise for axial piston pump is discussed. The noise reduction effect of the axial piston pump with this valve plate was analyzed by adopting a flow characteristic simulation model. Finally, the results showed that the application of this design method could contribute much to the reduction of the flow ripple and elimination of the pressure overshoot and undershoot. As a consequence, the method can be used in the design of a low-noise open circuit axial piston pump.

The paper analyzed the temperature field and the thermal stress field of a diesel engine piston with finite element analysis software ANASYS, then used the thermal mechanism indirect coupled method, researched the coupled stress field of piston. The result indicated that the point of the highest temperature located on the middle of firebox which under the dangerous temperature of the material; under thermal stress effect, the max displacement of the piston did not exceed the clearance between piston and cylinder liner, but the non-roundness at the third ring reached 0.08mm, which had some influence on the pressurize and lubricate of piston; under thermal mechanism coupled effect, the point of max stress located on the interface of the seat of the pin and the pin hole, so as the top on the pin hole and inner on the seat of pin, so it was recommended to set rib between cervix and the seat of pin of piston to enhance the practical carrying capacity of the seat of the pin.

In order to develop a new type of high-performance axial piston pump, the impact of the dynamic response characteristics of piston chamber pressure to the stability of cylinder block were analyzed. This paper a new type of valve plate which combined two fixed throttling grooves with a triangular groove (called three-level gain) was put forward so as to reducing the excessive pressure adjustment of the dynamic response of piston chamber pressure and improving the stability of cylinder block. The simulation results indicate that not only the cavitation is reduced, but also the stability of the dynamic response of piston chamber pressure is remained at various swash plate angle which makes it applicable to variable piston pump. The results also indicate that the flow pulsation of variable displacement pump is significantly decreased in different operating conditions.

To assess piston’s thermal loads, the direct and effective method is to calculate piston’s temperature distribution. A key point in calculating the temperature field of a piston is the determination of heat transfer boundary conditions of each side, especially the gas side. The thermal boundaries of a piston consist of the piston top side (combustion side), the crevice surfaces, the piston ring land and skirt outside surface, piston underside and pin hole side.The calculating methods for the heat transfer boundary conditions of engine piston are studied according to the theoretical analysis of heat transfer of engine piston, which can be taken as a reference for providing precise boundary conditions for the research on piston’s temperature field.

The intermittent transient contact of the piston skirt and cylinder liner is related to the secondary motion of the piston. The instantaneous piston secondary motion measured using laser displacement sensors can indicate whether the piston skirt is in contact with the cylinder liner. The force of the impacting piston skirt on the cylinder liner can be calculated using the equation of motion, which allows the piston skirt friction force to be distinguished from the total friction force and friction torque. The results showed that the piston skirt friction force contributes as much as 44% of the overall piston assembly friction force.

The piston slipper in an axial piston pump demonstrates most complicated dynamic motions: two rotations (tilting toward to the swash plate and rotating about the pump shaft) and one translation together with the pumping piston. In addition, the slipper is used to lubricate the swash plate surface with hydraulic oil, but prevents high pressure fluid escaping from the piston bores. In hydraulic engineering, improper designs of the piston and slipper assembly cause many instability and unbalance issues while the slipper attempts to lift and tilt off the swash plate. This may cause catastrophic failure and damage to a piston pump. To suppress the undesirable motion is one of most design difficulties that might take a range of different dynamics into consideration and compromise the design parameters of piston assemblies.In this study, the complicated dynamics are simplified and linearized with some assumptions that are able to apply stability conditions. The dynamic response of the assembly as operating needs...

To reduce the cavitation occurring on valve plate of typical Swashplate piston pump, an optimization design method was introduced to quantitively analyse the accurate relationship between structural jet grooves parameters and cavitation.Using the CFD method, the sunking and discharging process in piston pump was simulated dynamically.The damp grooves structure effect on both jet angle and pressure shock were analysed visually with a series of different parametrical grooves.By establishing parametrical damp groove model, the piston pumps dynamic analysis was integrated with the technologies of CFD analysis, experimental design and approximation model, etc.The mathematical model of plunger pressure in oil back period, jet angle and structural parameters of damp groove were established in the form of second-order RSM model. The damp groove structure of valve plate was optimized on the basis of the RSM model.Test data show that the anti-cavitation performance of optimized valve plate was increased obviouslyAnd this method provided theoretical foundation for the structure design of damp groove.

Based on the principle of hydrostatic bearing, in this study, several novel kinds of pistons were designed out, and the mathematic model of hydrostatic bearing on piston was established and analyzed. It was also found that, the diameter of damping hole and the width of pressure recess had impact on the radial load capacity of piston, the overall efficiency of axial piston motor, and the friction and wear capacity of piston. Results from tests shown that in the case of the pressure difference of 10MPa to 22MPa and the different speed of 500rpm to 2000rpm, the overall efficiency of axial piston motor could be improved by 0.1%-0.6%, compared to the ordinary piston. On the other hand, the wear scar of the piston modified was circular, and the one of the ordinary piston was longitudinal and deep, which shown that the piston modified could improve the wear capacity.

Hydraulic motor is an important hydraulic component in hydraulic control system, so the analysis of its performance is very important. The piston couple is one of the most important frictional pairs in axial piston motor, this paper studies the forces on the piston couple of swash-plate axial piston motor. It deduces the mathematical model of forces analysis in arbitrary phase of the cylinder, and the forces of a type of axial piston motor are analyzed. And it gives suggestions for structure optimal design of piston couple.

A nonlinear model of the piston with reciprocating, lateral and rotational degree of freedom is developed to investigate the piston secondary motion and the induced vibration behavior of the engine block by the piston slap. The model parameters are obtained from mobility measurement. The gap between the piston skirt and the cylinder liner is modeled as a translational hard stop which is the nonlinear component in the model. The value of the friction coefficient between the piston ring and the cylinder liner is determined by correlating the experimental data with the friction force equation. During the piston slap on the cylinder liner, the high damping coefficient and stiffness of the translational hard stop are added to the equation for the piston secondary motion. The model is validated by experimental data obtained from three laser displacement sensors which capture the distinct modes of the piston secondary motion directly from the piston assembly under motorized conditions. The predicted trend of the piston secondary motion and the vibration response of cylinder block are appropriate and compare well with the measured results.

As an initial step to develop a liquid hydrogen pump of piston type operated under cryogenic and high pressure, leakage and piston head shape for the piston pump were discussed with temperature and pressure. As the results, the leakage depended on correlation among density, viscosity, clearance area by the low temperature. In order to reduce the leakage, it was found that the air-tightness can be improved by minimizing contact surface between piston and cylinder, and also increasing pressure in-cylinder can reduce piston clearance. Among the proposed piston shapes, D type piston shape had the most air-tightness. D type piston had smaller contact surface than other piston shape and easier expansion of cup shape by pressure. The leakage of D type piston shape was found about 7%, compared with A type piston shape. But it was required that analyze about vapor lock by friction and wear resistance.

PurposeThe aim of this paper is to develop a technique to measure the oil film thickness between piston ring and liner throughout the stroke, without impairing the surface properties of the piston ring and liner. Mechanical properties of the piston ring, like ring stiffness, are also not altered. Effect of variation in bore on the movement of piston ring can be studied with the proposed technique.Design/methodology/approachThe gap Hmin between the cylinder liner and the piston ring is formed due to the hydrodynamic pressure generated by the presence of oil film between piston ring and liner. This gap can be inferred by measuring the movement of the inner surface of piston ring with reference to a sensor mounted on the piston at a fixed distance from the piston ring. The piston ring is connected to the sensor through reasonably rigid member. The underlying assumption here is that there is no elastic deformation of the piston ring due to the hydrodynamic pressure. The fundamental sensor to measure oil film thickness used in this setup is a set of strain gauges.FindingsIt is possible to measure oil film thickness by the proposed arrangement for the entire stroke without changing the surface properties. Mechanical properties of the piston ring, like ring tension, are not affected. The results possibly provide the correct picture of the piston ring movement throughout the stroke. The measurement at near zero speed can give information on the movement of the piston ring due to hydrodynamic action and to the variation in the bore. The measurement is not affected by engine vibrations. The proposed technique can be helpful in validating the theoretical models proposed in the literature.Originality/valueThe measurement is possible only in unfired condition. However, this attempt can be considered as the basis to measure OFT in fired condition with necessary improvements. It is not feasible to measure quantity of lubricant/extent of lubricant on leading or trailing edge of piston. Effect of temperature on the oil film thickness cannot be studied as the engine is not fired. It is assumed that the piston ring does not pass through elasto‐hydrodynamic lubrication regime. Debris/worn out particles in the oil may affect the indicated oil film thickness at local points.

Experimental studies on the overall efficiency performance of axial piston motor with a laser surface textured valve plate are developed to study the potential use of laser surface texturing in the form of spherical micro-dimples. This study adapts the fiber laser marking machine to machine micro-dimples with different dimensions on the surface of the valve plate for axial piston motor. In addition, these tests of the overall efficiency are given to the axial piston motor fixed to the valve plate with laser micro-dimples in order to find the relationship between the overall efficiency of the axial piston motor and different dimensions of micro-dimples on the surface of the valve plate. The regions of inner dead point and outer dead point of the valve plate are easily erodable because of the pressure pulsation. Therefore, in this study, micro-dimples are machined with different dimensions on the region of the valve plate for the axial piston motor. It is shown that the overall efficiency of the axial piston motor fixed to the valve plate with micro-dimples (area ratio of 5%) can be improved by 2.8%–6.1%, compared to that without micro-dimples; the overall efficiency of axial piston motor fixed to the valve plate with micro-dimples (diameter of 0.1 mm) can be improved by 0.8%–4.9%, compared to that without micro-dimples.

The limit working parameters and service life of axial piston pump are determined by the carrying ability and lubrication characteristic of its key friction pairs. Therefore, the design and optimization of the key friction pairs are always a key and difficult problem in the research on axial piston pump. In the traditional research on piston/cylinder pair, the assembly relationship of piston and cylinder bore is simplified into ideal cylindrical pair, which can not be used to analyze the influences of radial micro-motion of piston on the distribution characteristics of oil-film thickness and pressure in details. In this paper, based on the lubrication theory of the oil film, a numerical simulation model is built, taking the influences of roughness, elastic deformation of piston and pressure-viscosity effect into consideration. With the simulation model, the dynamic characteristics of the radial micro-motion and pressure distribution are analyzed, and the relationships between radial micro-motion and carrying ability, lubrication condition, and abrasion are discussed. Furthermore, a model pump for pressure distribution measurement of oil film between piston and cylinder bore is designed. The comparison of simulation and experimental results of pressure distribution shows that the simulation model has high accuracy. The experiment and simulation results demonstrate that the pressure distribution has peak values that are much higher than the boundary pressure in the piston chamber due to the radial micro-motion, and the abrasion of piston takes place mainly on the hand close to piston ball. In addition, improvement of manufacturing roundness and straightness of piston and cylinder bore is helpful to improve the carrying ability of piston/cylinder pair. The proposed research provides references for designing piston/cylinder pair, and helps to prolong the service life of axial piston pump.

International audience; In the design of high pressure piston pumps/motors, some manufacturers use pistons which have grooves being cut along the piston length, while others do not use grooves at all. The present paper clarifies the effect of grooves cut along the pistons surface via studding the effect of the number of grooves and their location over the piston surface. Piston force, torque, leakage, areas where cavitation might appear and piston stability, will be, in the present paper and for a set of piston/grooves configurations, carefully evaluated. A finite volume based Reynolds equation model has been formulated for the piston-cylinder clearance which considers the piston eccentricity and the relative tangential movement between piston and barrel. Different grooves configurations have been evaluated in search of finding minimum leakage, minimum appearance of cavitation and maximum restoring torque. Design instructions to optimize the piston behavior are also given, therefore the information and methodology presented in the present paper, is expected to be used as a designing tool for future machines. The piston/cylinder leakage is considered as laminar under all working conditions. The Fluid used is hydraulic oil ISO 32.

The four stroke otto engine uses just one of the four strokes to perform work. This causes various problems: The engine runs jerkily, and this can only be prevented by a large flywheel, which needs a lot of space and weights pretty much in addition. In this thesis, thermal loads and pressures produced in the multi cylinder petrol engine Toyota 86 Car by varying compression ratios 14:1, 15:1, 18:1, 20:1 and 25:1 are calculated by mathematical correlations And also calculating the effect of these thermal loads on piston and piston rings by varying materials Cast Iron, Aluminum Alloy 6061 for piston and Cast Iron and Steel for piston rings.FEA transient thermal analysis is performed on the parametric model to validate the effect of thermal loads on piston and piston rings for different materials. The optimum value of compression ratio and the better material is determined by analysis results to improve the heat transfer rate of multi cylinder engine piston and piston rings. Dynamic analysis is done on the piston by applying the pressures developed and also static analysis by applying the maximum pressure.

This paper introduces new type of save energy piston valve for water pump balance control, which is save energy efficiency expert. This piston valve is designed by pneumatic theory, and drive power is delivered by air compressor or pressure air source in waterworks. Pressure air is lead into cavity of piston valve by transfer action of “two positions and five channels ” electromagnetic valve, then piston drive valve to open or close water pump. This piston valve has followed functions such as balance control action, avoiding refluence, zero flow open and close, accidental power stop for water hammer and son on. Application of this piston valve had proved saving energy to 3%.

An asperity model between piston head and cylinder liner had been contained in the simulation of piston secondary motion. A prediction of wear of piston head has been made from the simulation which shows that the contact force of piston head is abnormal. The later engine installed experiment shows that the piston head is worn, which has confirmed this prediction.

On the basis of analyzing the working principle of the swashplate axial piston pump, based on the AMESim simulation platform, establishing the key components simulation models including the piston pump flowplate, the connector of swashplate and piston, swash plate control structure. In addition, use components of AMESim signal library to establish the complete piston pump model. By changing piston pump model parameters such as the export volume, the number of piston, the swash plate inclined angle, piston diameter, leakage crack size, operating simulation to get piston pump outlet flow and pressure fluctuation characteristic curve. The results show that piston pump pressure fluctuation can be reduced when increasing the piston pump export volume. Reducing the swash plate inclined angle, increasing the number of piston and reducing piston pump leakage can lessen the piston pump outlet flow fluctuation. Moreover, the relationship between the piston diameter and flow fluctuation is not obvious.

Piston/cylinder pair is one of the two most important friction pairs of bent-axis type piston pumps. The interface leakage of piston/cylinder pair has a great effect on the efficiency of bent-axis type piston pumps, especially for high-speed motion of piston/cylinder pair due to the extremely high centrifugal force and inertial force. In order to analyze and optimize the piston/cylinder pair precisely, a mathematical model on the piston/cylinder interface leakage of bent-axis type piston pumps is present. Full account is taken the centrifugal force and reciprocation inertial force of the piston/cylinder pair effects. The numerical method for the solution of the model is given, which can simultaneously solve the leakage rate in the interface. The influence of the centrifugal force and reciprocation inertial force on the piston/cylinder pair interface leakage is analyzed. Some of the conclusions provide suitable guidance for the design of bent-axis type piston pumps.

Modern design of the axial piston pump/motor, based on computer aided design, requires description of all processes and parameters in the pump/motor. The hydrodynamic and dynamic processes in the axial piston pump (cylinder, intake and discharge chambers, discharge valve, and high pressure pipeline) are very complex, so they demand a thorough physical and mathematical analysis. Compression losses, which are caused by sudden pressure changes in the cylinders of cylinder block, result in energy loss and increased noise. The compression losses can be decreased by identification of optimal dimensions and shapes of the port at the valve plate.

The structure and working principle of a new translational piston compressor was introduced in this paper. Its piston works in a way of translational motion, hence reduces the piston’s relative velocity to cylinder and cap, as well as friction and wear. In order to avoid vane detaching from piston, simulations were carried out regarding the pre-tightening spring and an optimal preload of the spring was obtained. By analyzed and compared to conventional rolling piston compressor in term of contact force between vane and piston, it was pointed out that the new compressor possessed advantage of kinetic characteristic and is more suitable for the situation of high rotary speed.

The internal energy of working fluid in Twin-Rotor piston engine is transmitted into mechanical energy by differential velocity movement between the couple of rotors coaxial installed. The blade piston, a part of the power transmitting mechanism, is the most important component working in the worst condition in the engine. It withstands heavy mechanical and thermal loads as working at a high rotating speed, that is to say it undertaking the explosive force straight and transmitting the power to power transmitting mechanism at the first time. So the section shape of blade piston on the rotor affects power output of the engine directly. In order to select the section shape of blade piston properly, improve output capacity and reduce the affect of deformation, models of several typical shapes of the blade piston is set up. Based on the comparison of aspect ratio, analysis and size optimization are performed. The results show that the rectangular cross-section blade piston is more efficient in power transmission with small deformation and larger torque as long as the values of aspect ratio are in a reasonable range.

Dynamic performance of a water hydraulic piston pump with flat valves was analyzed．Its mathematic model was established and influence factors were studied by simulation. The results show that reducing clearance volume, lighting spool quality and increasing spring stiffness are favorable to promote the performance of flat valve. In addition, higher vacuum degree and too high rotational speed will make flat valve delay more seriously. Work pressure also has influence on the opening delay to flat valve．

The secondary motion of the piston head of a motorized engine is captured using two laser displacement sensors to obtain the piston motion and tilt angle. The controlled parameters of the measurement are engine speed, quantity of oil and oil–fuel mixture and its ratio. The reduction in friction force is more significant at dead center at high speed as the quantity of oil supplied increases. Changes in tilt direction of piston head occur at the inlet port. The relationship between the friction force and piston tilt angle showed weak correlation at low speed and increases with the engine speed.

In this paper, we present a novel axial piston water-pump with piston valve, which carries out the flow distribution to drain and sucks water by the interaction of each piston. This novel water-pump could achieve change in-phase between flow rate and the passage areas of the intake and outlet ports. In order to completely achieve the in-phase change, the pressure that is assigned a fixed value in the piston chamber is optimized. On these grounds, the optimum shapes of the intake and outlet ports have been found to be rectangular according to theoretical analysis. The simulation results indicated that the optimum intake and outlet port shapes keeps the pressure in the piston chamber constant, and there is almost no pressure surge except for a very small pressure wave in the piston chamber. Finally, the test of model machine showed that the pressures of the intake and outlet port are very steady, but the leakage is large and the volumetric efficiency is 74.7%.

The movement characteristics of hydraulic exciting piston is a small displacement and high reversing frequency. The movement of the piston is to adapt to the requirement of quick reversing resistance. The mating surface seal uses to reduce the motion resistance to meet the requirements of the piston movement. Piston position should be in the oil chamber oil area to meet the requirements of the piston movement and oil circulation. Elastic beam with hydraulic cylinder is connected together . This structure is conducive to the piston and the connection of elastic beam and the installation of the oil cylinder. The causes of the different moving displacement of piston is leaking.

The bent-axis type of piston pump driven by the piston rod works by the piston rod driving the cylinder block; because of this the taper angle of the piston rod and the swivel angle between the cylinder block and the shaft are important design factors. If these factors cannot satisfy the conditions for optimum design, the friction loss between the cylinder bore and the piston increases, and the pump can fail to work under conditions of severe friction and wear. Since the piston reciprocates in the cylinder bore with high velocity, at the same time rotating on its own axis and revolving on the center of the cylinder block, a decrease of the volume efficiency is generated because of the leakage between the cylinder bore and the piston. Therefore, to prevent this, the piston ring is designed to be at the end of the piston, and the friction characteristics between the piston ring and the cylinder bore require further research due to their great influence on the performance of the piston pump. Thus, in this paper, the elastohydrodynamic lubrication (EHL) analysis of the film thickness, the pressure distribution, and the friction force, have been studied between the piston ring and the cylinder bore in the bent-axis type of piston pump. The analyzed results show that the friction force is influenced by the rotating speed and the discharge pressure.

A liquid piston concept is proposed to improve the efficiency of gas compression and expansion. Because a liquid can conform to an irregular chamber volume, the surface area to volume ratio in the gas chamber can be maximized using a liquid piston. This creates near-isothermal operation, which minimizes energy lost to heat generation. A liquid piston eliminates gas leakage and replaces sliding seal friction with viscous friction. The liquid can also be used as a medium to carry heat into and out of the compression chamber. A simulation is presented of the heat transfer and frictional forces for a reciprocating piston and a liquid piston. In the application of an air compressor, with a pressure ratio of 9.5:1 and a cycle frequency of 20 Hz, the liquid piston decreased the energy consumption by 19% over the reciprocating piston. The liquid piston and the reciprocating piston exhibited a total efficiency of 83% and 70% respectively. The liquid piston demonstrated significant improvements in the total compression efficiency in comparison to a conventional reciprocating piston. This gain in efficiency was accomplished through increasing the heat transfer during the gas compression by increasing the surface area to volume ratio in the compression chamber.

The advantages are described of a piston pneumatic motor (PM) over other types of PM. The scheme is presented for a piston direct-flow PM, in which the driven gas distribution system is replaced by a self-acting one. Working characteristics have been derived for a direct-flow PM with given design parameters in steady states. It is concluded that self-acting valves in piston PM provide for higher crankshaft rotation speeds because of their low inertia.

To improve the performance of the bent-axis type axial piston pump driven by the tapered piston, it is necessary to know the driving characteristics and mechanism of the tapered piston and the cylinder block. Since each piston not only rotates on its axis and reciprocates in the cylinder bore but also revolves around the axis of the driving shaft, it is difficult to analyze the driving mechanism theoretically. The theoretical mechanism for the bent-axis type axial piston pump is studied by using the geometrical method. The driving range of the tapered piston is determined by theoretical equations. The results show that the cylinder block is driven by one tapered piston in a limited range and the core parameters such as the tilting angle of the piston and the ahead delay angle influence performance of the bent-axis type axial piston pump.

In water hydraulic systems, requirements for better energy efficiency call for the development of variable displacement axial piston pumps. Most axial piston units utilizing water as pressure medium lack the possibility of adjusting the swash plate tilt angle because of difficulties in constructing robust water compatible swash plate pivot bearings. Without smooth enough adjustment motion, the lubrication conditions between the swash plate and the piston slipper pads become disturbed and loss of fluid film may lead to early pump failure. This study reports on measurements made with a test rig built for investigating tribological phenomena in variable displacement axial piston pumps. In the tests, the effects of changing the swash plate tilt angle were measured in a test setup with constant high pressure which loaded the piston. Lubricating film thickness and lateral force acting on the piston were measured together with changes in these quantities in response to changes in swash plate tilt angle.

A numerical analysis of a piston motion in a free piston driver has been conducted including a diaphragm rupture. Quasi-one-dimensional flow is assumed in the driver. Various losses, which are generated in a compression process, are simplified. A process of the diaphragm rupture is assumed by Outa’s model. Experiments are also conducted by using a free piston shock tunnel. Calculated pressure histories show excellent agreements with experimental results. The numerical analysis shows that the piston motion is strongly affected by the diaphragm rupture. Especially, pressure histories in front of the piston change significantly with compact compression tubes. Diaphragm opening time is necessary to be considered to increase test time and to obtain soft landing conditions in compact free piston drivers.

In this article, a previously developed and experimentally validated piston secondary motion model has been improved further numerically and applied to understand the detailed interactions between the piston skirt and the cylinder liner for various piston design parameters. The model considers the roughness of the surfaces and the topography of the skirt in both the axial (barrel profile) and circumferential (ovality) directions. Three modes of lubrication: hydro-dynamic, mixed, and boundary lubrication regimes have been considered and the skirt is partially flooded in most cases. Elastic deformation of the skirt is an essential part of the model. In this model, the piston dynamic behaviour and frictional and impact forces are predicted as functions of crank angle and are examined in detail. Parameters investigated include piston skirt profile, piston-to-liner clearance, surface roughness, and oil availability. The results show that some of these parameters have profound effects on the frictional and impact forces at the piston skirt/liner interface, and therefore, they have the potential to optimize the piston frictional power loss. Correlations and non-dimensional scaling laws are developed to illustrate the basic governing phenomena. These results aim to provide a set of quantitative design guidelines.

In this study, a numerical analysis for the piston secondary dynamics of small refrigeration reciprocating compressors is performed. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the variation in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the lubrication characteristics as functions of crank angle under compressor running conditions. The results explored the effects of some design parameters and operating conditions on the stability of the piston, the oil leakage, and friction losses.

Dynamic lubrication characteristics between a piston and a cylinder in an axial piston pump and motor have been calculated under mixed-lubrication conditions. The calculated results have shown that half-frequency whirling of the piston occurs under some operating conditions and specifications such as low supply pressure, narrow clearance and long sealing length between the piston and the cylinder, in a manner similar to the oil whirl phenomenon in journal bearings. The whirl phenomenon has been confirmed by measurements of piston motion.

For a reduction of period of piston development, it is very important to estimate the piston defects such as slap-noise and -vibration and skirt seizure induced by piston secondary movement and the difference of thermal expansion between piston and cylinder in engine running condition at the desktop stage. This paper describes the numerical simulation for prediction of the three dimensional skirt contact pressure and deformation in consideration of piston secondary motion. In this analysis, the iterference of piston skirt and cylinder was calculated by the geometrical consideration and reaction forces from cylinder was computed using stiffness matrix obtained in the experimental study. The validity of the results was verified by the comparison of the experimental results reported in the previous paper. After TDC firing, thrust side of the skirt was highly deformed by the piston slap.