Swashplate Type Axial Piston Pumps Research Articles

CFD Analysis of water-based slipper bearing

The leakage across the slipper land of a swashplate type axial piston pump is inherent in almost all the commercially available designs. This occurs due to the back flow of each piston through its orifice and gap between the slipper and swashplate. This flow phenomenon is studied in detail in the present work. To optimize pump performance with a reduced leakage, it is critical to know the fluid dynamics within the pump passages. In this paper, a three-dimensional CFD methodology has been created and employed to predict the pump performance in terms of pressure field, velocity vectors, and the flow pattern to understand pump flow. The methodology is established in the commercially available code ANSYS FLUENT 16.0 which supports the existence of complicated geometry in the form of narrow orifices and gaps between rotating and stationary walls. Slipper leakages, velocity and pressure fields are computed using simple algorithm approach at different designs and operating conditions. Experimental data of the film thickness is used in the present simulation. The effect of different piston pressure, slipper velocity, oil viscosity, slipper orifice diameter and slipper pool inner diameter is studied. Investigations of this kind may help for the development and design of slippers.

Effect of Operating Parameters on Efficiency of Swash-Plate Type Axial Piston Pump

In an effort to improve the energy economics of hydraulic systems, attention should be paid to reducing power losses in two main entities, energy converting components, and energy controlling and conveying components. Achieving the former requires utilizing components’ most energy efficient operating range. The energy converting efficiency of a pump, which is the primary energy converter in a hydraulic system, is determined by several operational factors. Of these, only pressure and rotational speed are normally considered, but also the fluid temperature and derived capacity with variable displacement pumps have a major effect on the efficiency. Omitting these factors may lead to running the pump outside its most efficient operation range and cause high energy losses. Operating the pump in its optimal region calls, however, for detailed knowledge of its performance characteristics, which are not generally made public by the pump manufacturers. This study presents the performance measurement results of a variable displacement axial piston pump in the form of efficiencies as a function of pressure, rotational speed, derived capacity and inlet fluid temperature. The results show that all of these factors have a significant impact on pump’s energy conversion efficiency and should, therefore, be taken into account when operating a hydraulic pump.

Numerical Simulation of a Slipper Model with Multi-Lands and Grooves for Hydraulic Piston Pumps and Motors in Mixed Lubrication

A theoretical model of a slipper with multi-lands and multi-grooves for swashplate type axial piston pumps and motors was established, including surface interactions. Further, a numerical simulation was conducted under an unsteady state and mixed lubrication conditions. Four model configurations were considered: A slipper with a single main land; a slipper with inner and main lands and a groove; a slipper with outer and main lands and a groove; and a slipper with inner, main, and outer lands with two grooves. Numerical solutions were obtained across a wide range of operating conditions in terms of center clearance, pad attitude, contact pressure, flow rate, friction torque, power loss, and stiffness. The motion and characteristics were differentiated into two groups: Slippers with a single-land and an annex inner-land; and slippers with an annex outer-land and a triple-land. The single-land and annex inner-land slippers exhibited smaller pad swing, whereas the triple-land and annex outer-land slippers reduced contact pressure and power loss.

Overall Efficiency Evaluation of a Hydraulic Pump With External Drainage Through Temperature Measurements

In the recent years, industries have been working on the online condition monitoring of systems and components in order to definitely abandon the time-based maintenance and switch efficiently to a condition-based maintenance. Therefore, the research field related to prognostics and health management (PHM) has been gaining more and more importance. In the field of hydraulic pumps and motors, the overall efficiency is an important parameter to monitor and the thermodynamic method has historically been proposed for the online evaluation of this parameter for hydraulic machines without external drainage. Indeed, for this kind of machines, the thermodynamic method allows the evaluation of the overall efficiency by measuring only the temperatures and the pressures at the suction and the delivery ports, thus avoiding the use of cumbersome and expensive sensors, such as flow meters and torque sensors. This paper investigates the use of the thermodynamic method for hydraulic machines with external drainage. The case study of a swash-plate type axial-piston pump is considered. In this first part of the project, the objective was to validate the proposed thermodynamic method by comparing its results with the ones obtained through the mechanical, therefore an extensive experimental activity was carried out and two flow meters were used to measure the drainage and the delivery flow rates. The pump was tested in different operating conditions and the uncertainty related to the overall efficiency was calculated accurately in order to compare the two approaches properly.

Thermohydrodynamic lubrication model of a slipper in swashplate type axial piston machines - validation through experimental data

A thermohydrodynamic lubrication (THL) model of hybrid (hydrostatic and hydrodynamic) thrust bearings, which is applicable to slippers of swashplate type axial piston pumps and motors, was validated by experimental results. The model consisted fundamentally of the generalised Reynolds equation, three-dimensional energy equation, and the heat conduction equation. The numerical calculation was performed in fluid film lubrication under the experimental conditions and the solutions were compared with the data. Reverse flow and oil mixing were considered in solving the energy equation. The comparison of the temperature distributions and centre clearances was made at supply pressures up to 35 MPa and rotational speeds up to 26.7 s–1. The simulation showed good agreement with the experiment and the theoretical model was validated.

Buoyancy engine developed for underwater gliders

A buoyancy engine with a swashplate-type axial piston pump was developed. Its oil extrusion and drawing properties under high hydraulic pressure were evaluated. This buoyancy engine is now installed in an underwater glider that will achieve long-term monitoring of ocean environments up to 2100 m depth in a designated area with lower operational costs. This bidirectionally functioning pump can control the amount of oil in extrusion and draw operations. When drawing oil under high pressure, the hydraulic pump and the electric motor, respectively, act as a hydraulic motor and an electric generator. The generated electric power is absorbed by a damping resistor. The oil-drawing and extrusion properties were measured using a large hyperbaric chamber that is able to produce an almost identical environment to that of actual operations. Results confirmed stable oil extrusion operations up to 21 MPa. Regarding oil-drawing properties, although it was measured only up to 10 MPa in the hyperbaric chamber, it can be inferred that the system can draw the oil and can control the buoyancy precisely up to 21 MPa by replacing the two-way ball valve with an electromagnetic latching solenoid valve.

B208 斜板式アキシアルピストンポンプ・モータのスリッパモデルに対する数値シミュレーション : 斜板振動の影響(OS3 フルードパワーの基礎と応用1)

Vibration of a swashplate in swashplate type axial piston pumps and motors is considered in the slipper model. The theoretical model is established in consideration of vibration of the counter surface of the slipper and the calculation is performed under unsteady mixed lubrication. The representative parameters are as follows: the supply pressure of 21 MPa, the rotational speed of 25 rps, the slipper radius of 10 mm, the revolution radius of 30 mm, and the oil viscosity of 32 mPa・s. The motion, flow rate, contact pressure, and power loss are shown and the effects of the swashplate vibration and the operating conditions on the tribological characteristics of the slipper are discussed.

Effect of surface non-flatness on the lubrication characteristics in the valve part of a swash-plate type axial piston pump

The objective of this application study was to investigate the effect of surface non-flatness on the lubrication characteristic of the bearing/sealing part between cylinder barrel and valve plate in a hydrostatic axial piston pump. A developed numerical algorithm facilitated the simultaneous calculation of time-varying cylinder pressure, rotating body motion, and fluid film pressure to observe fluid film geometry and power loss. It was shown that an ideally flat surface might not form full fluid lubrication film properly, and that small-scale machining error, surface waviness, may increase the film thickness to some degree. The shape model of surface waviness considered waviness unit shape as well as its surface lay. However the results demonstrated that surface non-flatness of such small scale did not form the desirable fluid film geometry which minimized the power loss yet. Providing some surface design tips, two particular curved surfaces whose pressure-generating mechanisms differ were selected and analyzed in variation with their shapes and operating conditions. This study asserted that a circumferentially wavy surface would make better performance of motion stability and power efficiency than a radially wedged land surface, and finally that the non-flatness design strategy should be applied with re-considering the clamping ability.

Calculating Method for the Leakage between Slipper and Swashplate in Spherical Swashplate Type Axial Piston Pump with Conical Cylinder

This paper takes the piston that has tapered rotor spherical axial swashplate as the research object, aiming to develop research of calculation of slipping shoe and the swashplate of the lubrication circular leakage. First , analyzing the structure of piston pump that is characterized by slipping shoe static pressure lubrication, Based on the continuum of fluid , component force of slipping shoe as well as the pressure force gives rise to equations in which the Annular aperture fluid thickness and leakage are taken into calculations. Through detailed deductive calculations, the specific algorithm formula is given. Taking a certain Aero fuel piston pump as an example for developing slipping shoe circular leakage volume that changing with the structural parameter simulation. An analysis with the simulation curve illustration proves that the algorithm is available to the pump, and it is valuable and reasonable for slipping structure as well as the design.

Novel Piston Pressure Carryover for Dynamic Analysis and Designs of the Axial Piston Pump

The timing definition of valve plates is one of the most complex topics in the piston pump designs because it affects many pump characteristics (such as efficiency, swashplate stroking, stabilities, noise, etc.). In the study, the pressure carryover is introduced and defined as the average angular positions to locate piston pressure transitions from the top dead center (TDC) or bottom dead center (BDC) in the piston pump. Pressure carryover presents the overall outcome of the pressure transitions within piston bores. The new pressure carryover definition is derived by the timing angles and other geometrics of valve plates that is an approximation of the practical pressure transitions. The pressure carryover also determines the containment forces and moments on the swashplate produced by the pumping pistons. The relationship between the pressure carryover angle and the containment moment has been developed and analyzed in the study. The amplitudes and frequencies of the forces and moments can be changed by varying the pressure carryover angle that produce different tonalities and control efforts for the swashplate type axial-piston pumps. Therefore, the pressure carryover is the most important and straightforward connection between pump dynamics and valve plate designs. In order to optimize the pump performance, the piston pressure carryover might be investigated thoroughly for the pump and its controller designs.

The Slipper Shoe Mounting Hole Calculation Method Limitation Analysis for Spherical Swashplate Type Axial Piston Pump

Take conical cylinder spherical swashplate type axial piston pump as research object, the calculation method limitation of slipper shoe mounting hole which located in mounting plate is analyzed. First of all ,the motion characteristics and the trace of slipper shoe is derived, then,based on above results, the sipper shoe mounting hole size current calculation methods in engineering and it’s limitations is analyzed,the conclusion is that: current design methods is parameter averaging method and also is an approximate method, in theory is not accurate and in engineering is unreasonable. In order to deign the slipper shoe mounting hole accurately, this paper recommends the most reasonable method is using slipper movement envelope to determine its shape and size.

표면가공무늬가 사판식 액셜 피스톤펌프의 밸브부 윤활특성에 미치는 영향에 관한 연구

This application study of a swash-plate type axial piston pump was concerned about the lubrication characteristics between cylinder barrel and valve plate which are the main rotating body and its opposite sliding part respectively. A computer simulation was implemented to assess bearing and sealing functions of the fluid film between cylinder barrel and valve plate. A numerical algorithm was developed to facilitate simultaneous calculations of dynamic cylinder pressure, 3 degree-of-freedom barrel motions considering inertia effect, and fluid film pressure assuming full fluid film lubrication regime. Central clearance, tilt angle, and azimuth angle of the rotating body were calculated for each time step. Surface waviness was found to be an influential factor due to the small fluid film thickness which can appear in flat land bearings. Five surface lays which can form on the lubrication surface in accordance with machining process were defined and analyzed using the simulation tool. Oil leakage flow and frictional torque in the fluid film between cylinder barrel and valve plate were also calculated to discuss in the viewpoint of energy loss. The simulation results showed that in actual sliding conditions proper surface non-flatness can make a positive effect on the energy efficiency and reliability of the thrust bearing.

사판식 액셜 피스톤 펌프에서의 압력맥동 해석모형에 관한 연구

Although swash-plate type axial piston pumps have the merits of wide operating conditions and high efficiency, the characteristics of pressure pulsation and flow ripple which result in system noise generation are on-going problems. This research examined the analytic models of the dynamic oil pressure and flow characteristics in the pump. A new mathematical model which considered the pressure behaviors of each cylinder and discharge piping was developed to analyze the pump pressure and flow. This model also considered the leakages in the clearances which many researchers have ignored so far. Using the developed model, numerical calculations were implemented. The results showed that widely used simple model which considered only a single cylinder can not predict actual discrete flow dynamics and that fluid inertia effect has to be considered in the mathematical model. Several critical parameters were discussed such as port volume and discharge resistance on the assumption that the pipe length is not so long. The effect of leakages was studied on the final stage.

The Slipping Shoe Motion Trajectory Analysis and Simulation of Spherical Swashplate Type Axial Piston Pump

Spherical swashplate type axial piston pump slipping shoe hole shape and reasonable position design is key points for pump working. Current calculation method which adapted average parameters as final size is not accurate in theory. In this paper ,according to the relationship between geometry and motion of piston pump, coordinate transformation is used three times to deduce motion trajectory equation,and drive motion trajectory curve. The method discussed is precise ，it can be used to provide reference for slipping shoe hole design.

Thermohydrodynamic Lubrication Model Applicable to a Slipper of Swashplate Type Axial Piston Pumps and Motors (Effects of Operating Conditions)

A thermohydrodynamic lubrication (THL) model of a hybrid (hydrostatic and hydrodynamic) thrust bearing is developed. It is applicable to a slipper of swashplate-type axial piston pumps and motors. The generalized Reynolds equation, three-dimensional energy equation, and the heat conduction equation are derived. Physical properties such as density, viscosity, specific heat at constant pressure, thermal conductivity, and thermal expansivity of a hydraulic oil are considered as functions of temperature and pressure. The effects of the operating conditions on the temperature rise, clearance shape, and the power loss are shown. The numerical parameters are specified for the fluid-a hydraulic oil with ISO VG 46-supply pressure 7-21 MPa and rotational speed 15-60 rps. The solutions between the slipper model and the circular hydrostatic thrust bearing as well as between the THL and isothermal (ISO) solutions are compared. Increases in the supply pressure, rotational speed, and the revolution-radius increase the maximum temperature and the power loss. Furthermore, the discrepancies between the THL and ISO solutions increase. The rotational speed affects characteristics more than the supply pressure.

Robust control of the pressure in a control-cylinder with direct drive valve for the variable displacement axial piston pump

To achieve energy-efficient hydraulic systems, an accurate flowrate and pressure required by a load should be supplied to the systems. The discharge flow from the variable displacement swash-plate type axial piston pump is mainly determined by the angle of the swash-plate and it is adjusted by controlling the pressure in the control cylinder, which is a mechanical regulator for the swash-plate. In this paper, a robust pressure control system of the control cylinder using a direct drive valve is proposed to control the discharge flow from the variable displacement swash-plate type axial piston pump precisely. In order to design a robust pressure control system, a mathematical model of a pressure control system is derived and system parameters are identified by using the signal-compression method. Also, the sliding mode controller is designed based on the identified mathematical model to guarantee the control performance of the pressure control system. Experiments verified the satisfactory performance of the proposed pressure control system that uses a direct drive even with non-linearity and uncertainties such as flow characteristics, unknown discharge coefficient of the valve orifice, variation of the bulk-modulus, leakage, and disturbance induced by the pressure fluctuation in the pressure control system.

ハイブリッド・スラスト軸受の熱流体潤滑解析（斜板式アキシアルピストンポンプ・モータに用いられるスリッパのモデリング）

A thermohydrodynamic lubrication (THL) model of hybrid (hydrodynamic/hydrostatic) thrust bearings for a slipper of swashplate type axial piston pumps and motors is developed. The generalized Reynolds equation, three-dimensional energy equation and heat-conduction equation are derived, and the physical properties (density, viscosity, speci.c heat at constant pressure, thermal conductivity and thermal expansivity) of a hydraulic oil are considered as functions of temperature and pressure. The equations are solved numerically, and the THL solutions of the slipper model are compared with the isothermal solutions and the solutions of the circular thrust pad hydrostatic bearing. The e.ects of the physical properties, the revolution radius and the slipper spin on the temperature distribution, temperature rise, clearance shape and power loss are examined for both of the THL and isothermal analyses. The physical property changes in.uence on the characteristics of the slipper model rather than the characteristics of the circular pad bearing model. The THL solutions indicate that an increase in the revolution radius causes an increase in the .lm temperature and the pad inclination.

TEMPERATURE MEASUREMENT OF TRIBOLOGICAL PARTS IN SWASH-PLATE TYPE AXIAL PISTON PUMPS

Temperatures of a swash plate, cylinder block, and a valve plate of swash-plate type axial piston pumps with a rotating cylinder block and a rotating swash plate were measured. Thermocouples were embedded underneath these parts. Hydraulic mineral oils with ISO VG22, 32, 46, and 68 and a water-glycol type hydraulic fluid with VG32 were used as test fluids. The maximum discharge pressure was 20 MPa and the maximum rotational speed was 28.3 rps. The inlet oil temperatures were specified as 293-313 K. At the atmospheric pressure to the maximum discharge pressure, the temperatures, flow rates, and the torque were measured. Results support the following conclusions: i) as the discharge pressure increased, the temperatures of the swash plate, cylinder block, and the valve plate increased in almost direct relation; ii) the cylinder block temperature at the bottom dead center of the pistons increased markedly; iii) the temperature increases using the water-glycol fluid were noticeably smaller than the rises using the mineral oils; and iv) the temperature rises became large for higher fluid viscosity and lower inlet oil temperature.

3161 アキシアルピストンポンプの斜板・シリンダブロック・弁板しゅう動部の同時温度計測(S35-3 機械要素の設計・製造・応用技術(3) 軸受及びしゅう動要素の特性,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Temperature of three main tribological parts of a swashplate type axial piston pump was measured simultaneously. Five thermo-couples were embedded in the cylinder block, four thermo-couples were in the swash plate, four thermo-couples were in the valve plate and one thermistor was placed in the suction conduit. A hydraulic mineral oil with ISO VG22 was used as the test oil. The maximum discharge pressure was 20 MPa, the maximum rotational speed was 25 rps, and the inlet oil temperature was 20, 30, 40 ℃. In conclusion, the temperature of the cylinder block near the bottom dead center of the pistons was high and the temperature near the top dead center was low; The temperature rise in the valve plate and the swash plate corresponding to the delivery port was large and the rise to the suction was small; The temperatures increased as the rotational speed became large; The cylinder-block temperature was less affected by the inlet oil temperature.

NUMERICAL SIMULATION OF A SLIPPER MODEL FOR WATER HYDRAULIC PUMPS/MOTORS IN MIXED LUBRICATION

This paper presents a time-dependent mathematical model of a hybrid (hydrostatic/hydrodynamic) thrust pad bearing as a slipper of swash-plate type axial piston pumps and motors for the use of tap water under mixed and fluid fihn lubrication condition. Effects are examined of the load eccentricity, time-lag of changes in the supply pressure and load, surface roughness, recess volume, and the revolution radius. The bearing's motion is simulated three-dimensionally, including roughness interaction and asperity contact. Solutions are obtained regarding the friction, flow rate, power loss, and stiffness. Calculations indicate that the eccentric load causes local contacts. The preceding change in the load poses a larger motion of the bearing. The hydrodynamic effect becomes marked as the revolution radius increases. As the recess volume increases, the bearing stiffness decreases.