Swash Plate Type Axial Piston Research Articles

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.

Computer Aided Optimization of Bearing and Sealing Gaps in Hydrostatic Machines—The Simulation Tool Caspar

AbstractThe simulation tool CASPAR (Calculation of swash plate type axial piston pump and motor) is presented in this paper. Based on the simulation of the flow through the lubricating gaps in swash plate type axial piston machines the pressure, velocity and temperature fields in the considered gaps can be determined. This allows the calculation of the main losses generated in the machine due to viscous friction and gap flow. The individual gaps are connected in a complex way to each other. The calculation of the gap flow requires the determination of the instantaneous gap heights for all considered gaps. This is realized by solving the motion equation for all moveable parts of the rotating group. For determination of pressure dependent external forces the instantaneous pressure in the displacement chamber is calculated simultaneously. The program further calculates the instantaneous inlet and outlet flow of the swash plate machine for pumping and motoring mode as well as internal volumetric losses.

可変容量形ピストンポンプの加振力補償による騒音低減 補償効果の実験的検証

This paper deals with active noise control of a variable displacement swash plate type axial piston pump. The primary cause of noise generation of a piston pump is the exciting force due to sudden pressure change in the rotor cylinders. We tried a new method to compensate the pump exciting force by activating two built-in control cylinders using an electro-hydraulic servo valve and sinusoidal signals synchronous with the pump rotation. This method is not to suppress the exciting force itself but to prevent it from vibrating the pump and consequently to reduce the peak level of frequency components of the pump noise. Through the experiments, the exciting force compensation has been verified to be effective for noise reduction of a pump. The noise level could be reduced, for example, to 68 dB from 74 dB for the pump equipped with rubber vibration isolators, and to 70 dB from 82 dB without isolators.

Investigations of the Temperature Behaviour of the Piston Cylinder Assembly in Axial Piston Pumps

In this paper the temperature behaviour of the piston cylinder assembly in swash plate type axial piston pumps is investigated. For the theoretical investigations a mathematical model is used that allows the calculation of the nonisothermal gap flow between piston and cylinder. For this purpose the Reynolds Equation, the energy equation and the equations of motion have to be solved. The gap flow and the pressure distribution in the gap is calculated by solving the Reynolds Equation numerically with a finite volume method. The temperature distribution is obtained by solving the energy equation over the piston cylinder assembly also numerically with a finite volume method. It is known that the piston undergoes an eccentric motion in the cylinder that has a significant influence on the gap flow. To calculate this motion a simplified equation of motion, based on the external forces, the hydrodynamic forces and the forces caused by elastic deformation, is used. A method is described that combines the calculation of these three equations and that allows calculation of the gap flow and the temperature distribution in the assembly depending on the design and the operating parameters of the machine. The experimental investigations were made on a standard pump that was modified for the measurements. The temperature distributions in the whole cylinder block of the machine and the dynamic pressure in the displacement chamber were measured under real operating conditions using a telemetry unit. The results were used to verify the simulation model.

A Study on Hydraulic Control Characteristics of a Swashplate Type Axial Piston Pump-Regulator System by Linearization Analysis

The regulator system has been modeled and combined to a swashplate type axial piston pump. Linear approximation has been performed for nonlinear coefficient terms of an axial piston pump-regulator model without significantly affecting accuracy. Based on the mathematical model of an axial piston pump-regulator system, a couple of characteristic curves of negative flow control and horsepower control are drawn, which show a good correlation with those of experimental results. So the simplified axial piston pump-regulator model in this paper is expected to be utilized not only for the design and analysis of hydraulic circuit of excavator but also for prevention of engine overload

Characteristic Experiment of Swashplate Type Axial Piston Motor (I)

The purpose of this study is to construct a testing equipment with which several characteristics of the domestically developed swashplate type axial piston motor can be tested and to develop a software with which the data from experiment can be stored and can be applied. The results of the study are as follows; 1) The leakage flow and the torque of the motor being stopped is propotional to supply pressure and their relation can be showed by linear equations. 2) The motor movement is not smooth below 50 rpm but it moves smoothly up 170 rpm. 3) When the motor starts or stops, the pressure rise ratio effects decisively to the max. torque.

斜板式油圧ポンプ・モータのスリッパ軸受の作動特性に関する基礎的研究

The performance of slipper bearings in the swash plate type axial piston pump/motor is analyzed theoretically under quasi-static operation conditions. The effect of the nonflatness of the bearing surface due to wear at the bearing periphery, which may be caused by contact of the bearing with swash plate during operation of the device, is taken into account as an essential factor for successful bearing operation. The attitudes, such as floating height and tilt angle, of the slipper bearing are calculated for given operation conditions, and the results obtained are presented in a characteristic diagram for bearing operation. It is also shown that thermal distortion of the bearing pad may possibly be a key factor for stable bearing operation.

On the efficiency of the axial piston motor considering piston form deviations

Axial piston motors rely on a close fit of piston to bore to minimise leakage past the piston due to axial pressure drop. Machining imperfections in the cylinder bore and the piston change the clearance between them, affecting the performance of the motor. The effect of machining imperfections like out-of-roundness and taper in the piston on the mechanical and volumetric efficiency of the motor, in the speed range where the viscous friction is dominant, are studied. Experiments to measure torque and leakage flow are conducted on a fixed displacement swash plate type axial piston hydraulic motor and results are presented.

DEVELOPMENT OF HIGH PERFORMANCE COMPONENTS FOR POLLUTION FREE WATER HYDRAULIC SYSTEM

In order to construct water hydraulic systems for environmental protection, we have developed a pollution-free water hydraulic pump and a water hydraulic servo valve. With a view to secure the same efficiency as oil hydraulic systems, we used a swash plate type axial piston pump, a spool type servo valve, and all parts are lubricated with water which is the hydraulic fluid. The system is made of ceramics, plastics, and so on. The water hydraulic pump has a mechanical efficiency of 94%, a volumetric efficiency of 86%, a power-to-weight ratio 1.0kW/kgf at the pressure of 21MPa, and a rotation speed of 1800min-1 The water hydraulic servo valve has leakage of under 760cm3/min and a response of 47Hz at a pressure of 21MPa. These components have the same performance as oil hydraulic system.

Mixed Lubrication Characteristics Between the Piston and Cylinder in Hydraulic Piston Pump-Motor

This paper presents a method for evaluating the lubrication characteristics between the piston and cylinder in a swash-plate type axial piston pump-motor under mixed lubrication conditions. A numerical analysis is carried out in order to obtain the metal contact force between the piston and cylinder, and the contact ratio λ is shown to represent the mixed lubrication condition both for the pump and the motor strokes. The contact ratio, λ, is also obtained experimentally by detecting electric resistance between the piston and cylinder in a practical swash-plate type machine. The experimental result is expressed by a relationship between λ and SO (the ratio of dynamic pressure to supply pressure) as indicated by the numerical analysis. In conclusion, the mixed lubrication characteristics between the piston and cylinder in a swash-plate type pump-motor is expressed by λ−SO curve irrespective of the operating conditions such as the supply pressure or the rotation speed.

A new prediction method of operating moment and cylinder pressure of a swash plate type axial piston pump

A new prediction method of operating moment and cylinder pressure of a swash plate type axial piston pump

A CAD expert system for axial piston pumps

In this paper, a CAD expert system for the design of swashplate type axial piston pumps is presented by embedding expert system techniques to the conventional pump CAD system. With the help of a modern and powerful expert system developing tool CLIPS, the design knowledge base and inference engine is constructed. The system has integrated three parts-design, performance simulation and drawing output. It has been verified that the CAD expert system is practical and efficient in the design process.

Lubrication between the Valve Plate and Cylinder Block for Low-Speed Conditions in a Swashplate-Type Axial Piston Motor.

It has become very important to improve hydraulic motor efficiency, especially in the low speed ranges, for finer operation. From this point of view, this report aims to provide technical data to help improve swashplate-type axial piston motor performance, particularly concerning the leakage and oil film thickness fluctuation between the valve plate and cylinder. The factors on their fluctuation were analytically examined. In the analysis, the friction loss between piston and cylinder, the accuracy of the motor shaft and rigidness of the motor shaft were regarded. The analytical results were in qualitative agreement with the experimental results.

斜板式アキシアルピストンポンプ・モータの低速時におけるピストン〜シリンダ間潤滑状態 （観察および評価）

Lubrication between the piston and cylinder of a swashplate type axial piston pump or motor affects performance greatly. It is desirable to make fluid lubrication condition in this sliding parts so that to decrease friction and abrasion. Understanding the lubrication condition between the piston and cylinder is very important to make optimal fluid lubrication in wide operating ranges.In this report, degree of metal contact or separation based on fluid film between the piston and cylinder is observed by measuring separation voltage (contact electric resistance) under a constant voltage applied across the piston and cylinder. Further, effects of each operating condition and radial clearance between the piston and cylinder is examined by evaluating lubrication condition using data processing by a personal computer.

斜板式アキシアルピストンポンプ・モータの低速時におけるピストン〜シリンダ間潤滑状態 ピストン形状の影響および強制潤滑の効果

Lubrication between the piston and cylinder of a swashplate type axial piston pumps and motors produce large effect on their performance. It is desirable that make fluid lubrication condition in this sliding parts to decrease friction and abrasion. Understanding of lubrication condition between the piston and cylinder is very important to make fluid lubrication condition in large operating ranges. Therefore, we proposed observing and evaluating the degree of metal contact and separation based on fluid film between the piston and cylinder under mixed lubrication condition. This method of observation and evaluation were announced.In this report, influence of radial clearance and piston shape are cleared, and give consideration to improvement of lubrication condition between the piston and cylinder. Further, the effect of the forced lubrication is examined.

斜板式アキシアルピストンモータ用静圧スリッパ軸受の起動・微速時漏れ特性の実験的研究

The problem in the study assigned was improvement of the swash-plate type axial piston motor, especially its starting and low-speed performance. The aim of this report is to provide technical data to help explain these problem points and increase overall efficiency. The lubrication of some sliding parts, which used hydrostatic slipper bearings, was considered to be an important problem. It is thought that the leakage characteristics of the hydrostatic slipper bearing produces a large effect on this motor's characteristics. Therefore, we carried out a theoretical analysis about leakage characteristics of the hydrostatic slipper bearing at the starting condition. The results of the theoretical analysis were announced.In this report, the leakage flow rate is measured with test equipment of the same scale as an actual commercial motor. The leakage characteristics of the hydrostatic slipper bearings at starting and low-speed conditions are cleared quantitatively. Further, the propriety of theoretical analysis is proven with a comparison between experimental and theoretical results.

零傾角近傍における可変容量形斜板ピストンポンプの特性 （第２報 零傾角復帰方向のモーメントの理論解析）

零傾角近傍における可変容量形斜板ピストンポンプの特性 （第２報 零傾角復帰方向のモーメントの理論解析）