Swash Plate Angle Research Articles

An investigation into the micro-geometric tapered-shape surface design of the piston bore of a piston–cylinder interface in an axial piston motor

Abstract. In pursuit of design solutions that reduce energy loss and improve wear resistance for the piston–cylinder interface in an axial piston motor, a fluid-structure interaction numerical model and a new test rig of the friction force of the piston–cylinder pair are developed to achieve the analysis and design of the micro-geometric tapered-shape surface of a piston bore. The piston bore with the tapered-shape surface axial distribution length ratio of 49.44 % of the overall length is found to be the relatively optimized one. Furthermore, how the shaft speed, load pressure, and swash plate angle influence the performance of the two-type interface is analyzed. Numerical analysis results show that, compared with the traditional cylindrical piston bore design, the piston–cylinder interface with the optimized tapered-shape piston bore in the axial piston motor can achieve a significant reduction in leakage flow and friction force, and the experimental results are consistent with the simulation results.

Analysis of the Influence of Structure and Parameters of Axial Piston Pump on Flow Pulsation

In view of the working principle of a swashplate axial piston pump, a simulation model of the piston pump was built in AMESim and its output flow pulsation characteristics were simulated and analyzed. We mainly analyzed the influence of the speed of the prime mover, the swashplate angle, the diameter of the piston, and port plate structure on the flow pulsation of the piston pump. The result of this research shows that the port plate structure, the swashplate angle, and the speed of the prime mover have an important influence on the flow pulsation of the piston pump. In order to effectively reduce the flow pulsation generated by the piston pump and reduce the noise generated in the process of flow distribution, the opening of the pre-compression angle and misalignment angle of the port plate of the piston pump must be reduced appropriately and the swashplate angle and the rotation speed of the prime mover should be controlled within a certain range. The flow pulsation of the axial piston pump decreases with the increase of the piston number and the decrease in the misalignment angle. The research results provide a reference for reducing the flow pulsation of the axial piston pump.

Characteristics of high energy-efficient Electro-hydraulic power source driven by servo motor and variable pump

An electro-hydraulic power source is a unit that provides power for a hydraulic system, whose energy efficiency determines the whole system’s energy efficiency. The electro-hydraulic variable displacement proportional pump has the disadvantages of bad controllability, slow dynamic response in low-pressure condition, and high energy consumption in its non-working period (due to its electric motor still running at a rated speed). The electro-hydraulic variable displacement pump has some drawbacks regarding bad controllability. Aiming the above problems, a new electro-hydraulic power source based on pressure-controlled variable piston pump driven by a servo motor is developed in this paper. The pump’s output pressure can be continuously controlled without throttle losses through changing a swash-plate angle of the pump, and the output flow can be continuously controlled by changing motor speeds. A simulation model is established based on the mathematical models of pressure-controlled pump and servo motor, and the characteristics of its constant pressure control and constant flow control are discussed. A test bench is built to study its characteristics of pressure control, flow control, and energy efficiency. The results show that: (1) the proposed power source can realize the pressure control of the system, the direct open-loop control performance of the electro-hydraulic pilot valve is better than that of the speed-variable proportional-integral closed-loop control; (2) the leakage caused by load pressure change can be supplemented by speed and the control accuracy error is lower than 0.2%; (3) under the situation of pressure maintaining without flow outputs, pressure unloading and constant pressure control operating, through controlling the motor speed, the energy consumption of the power source can be reduced by almost 30% compared to a traditional power source.

Relative motion relationship and collision mechanism of slipper-retainer assembly of axial piston machines

Under high-speed rotation, the retainer-slipper assembly has serious collision interference, which affects the performance of the key friction pair of the piston pump. And abnormal wear of the retainer and slipper is observed in the faulty piston pump, even with fracture of the retainer and severe wear of the slipper neck. Based on the master-slave principle of the slipper and the retainer, a mathematical model of the relative motion relationship between the slipper-retainer is established. And the collision law between the slipper and the retainer is obtained by combining the relative motion velocity equation of the slipper. The effects of swashplate angle and pump shaft speed on the relative motion trajectory and collision strength of the slipper-retainer assembly are analyzed. The coordinates of all contact points between the slipper and the retainer during one piston cycle are calculated. These results clearly show the friction area of the retainer hole. Researches show that the rotation angle of the power slipper at the transition point is reduced with increasing swashplate angle. The increase of pump shaft speed has no influence on the contact law of the assembly. The collision strength of the assembly increases with the swashplate angle and pump shaft speed. A parametric investigation of the contact and collision between the slipper and the retainer is realized, providing a design method for analyzing the wearing character and mechanical properties of the axial piston pump.

Fault Modeling and Simulation of Engine Driven Pump in Aircraft Hydraulic System

Abstract The structure of engine driven pump in aircraft hydraulic system is complex, its fault forms are diverse, and the fault transmission path is complex and multi factor coupling. In view of the above problems, based on the in-depth analysis of the working principle of the engine driven pump, the engine driven pump model is established, and the leakage fault injection mechanism of the friction pair is added. The relationship between the flow fluctuation characteristics of engine driven pump and the changes of pump spindle speed, swashplate inclination and pump outlet cavity volume are obtained through model simulation analysis. The mechanism of internal leakage fault of plunger pair, port pair and slipper pair are analyzed, the influence of leakage clearance parameters on key performance indexes such as pump pressure and flow are simulated, and the simulation test data of internal leakage fault of pump are obtained. The simulation results show that the inclination angle of swashplate and spindle speed are positively correlated with the output flow of the pump. The increase of pump outlet volume can effectively alleviate the pressure and flow fluctuation behind the pump. In addition, when the radial clearance of the plunger pair of this type of pump exceeds 0.2mm, the pump fault characteristics begin to appear. At the same time, the load change behind the pump will affect the characterization of the fault of internal leakage of the pump.

A study of piston and slipper spin in swashplate type axial piston machines

A common assumption in the analysis of swashplate type axial piston machines (APMs) is to consider the relative rotation between the piston and cylinder block almost equal to the shaft speed. While this effect has been observed experimentally and confirmed by simplified models, an in-depth study and confirmation of the causes has never been undertaken. To address this, the presented work performs a simulation study of the piston and slipper spin in APMs. For this purpose, this work first develops a strongly coupled simulation model considering the displacing action of the machine coupled - with asynchronous time stepping - with the detailed simulation of its lubricating interfaces. The proposed approach accounts for the dynamics of the floating bodies in these machines, the ball-socket friction which couples the dynamic of each piston and slipper, and the impact on the fluid-structure induced cavitation and mixed lubrication in their tribological interfaces. As a consequence, the mutual interaction between the slipper-swash plate interface and the piston-cylinder interface of the APM is taken into account. After validating this model on a reference commercial unit, the impacts of the operating parameters (such as instantaneous displacement, pressure and shaft speed) and of the ball socket friction on the behavior of the machine are explored. It can be observed from the simulation results that the relative piston rotary motion in the cylinder bore varies with the operating conditions and the swashplate angle is one of the most influential parameters.

Hydraulic axial plunger pump: gaseous and vaporous cavitation characteristics and optimization method

Gaseous and vaporous cavitation have extremely harmful effects on hydraulic axial plunger pumps, reducing flowrate and increasing flow pulsation. The collapse of vapor bubbles strongly impacts the inner wall and produces many pits. Therefore, it is very important to reduce gaseous and vaporous cavitation to improve the performance of hydraulic axial plunger pumps. In this work, a full cavitation model and a compressible model are used to simulate the two kinds of cavitation, which are validated by a series of experiments. It is found that the vapor and gaseous bubbles in the plunger chamber collapse owing to pressurization caused by the water hammer effect. The results show that a better combination of plunger chamber radius and swash plate angle can reduce the two kinds of cavitation when the theoretical flowrate is unchanged; increasing the angle of the inlet of valve plate can effectively reduce its cavitation and increase the filling mass of plunger chambers; increasing the angle of the relief groove can significantly reduce its vapor and gaseous volume fraction. The results can provide a useful reference for reducing gaseous and vaporous cavitation in the optimization and design of hydraulic axial plunger pumps.

Design and Modeling of an Impulse Continuously Variable Transmission with a Rotational Swashplate

A novel mechanical impulse continuously variable transmission (ICVT) is developed to provide continuously variable speed ratios and smooth acceleration for drivetrains based on a rotational swashplate, and its design principle is illustrated. A swashplate-guide linkage mechanism is used in the ICVT; the speed ratio of the ICVT is changed with the swirl angle of the rotational swashplate. A slider–linkage system, whose mo-tion is controlled by a speed-regulating handle, is used to adjust the swirl angle of the swashplate. A planetary gear system converts the regulated rotational speed of the swashplate to the output shaft of the ICVT. The speed range of the ICVT can be scaled up by coupling planetary gear sys-tems with different speed ratios. Overrunning clutches are used to rectify the rotational speed from the swashplate-guide linkage mechanism to ob-tain the output speed of the ICVT. Since the rotational swashplate can in-troduce large impulse rates of the instantaneous speed ratio, a connecting linkage is used to reduce the impulse rate and unbalanced inertial forces of the ICVT. Experimental tests of the output speed of the ICVT with four guide linkages verify the feasibility of the design and operation perfor-mance of the ICVT.

Modelling of the Micro Lubricating Gap Geometry Between Valve Plate and Cylinder Block in an Axial Piston Pump

The paper focuses on the effect of force and torque balance (FTB) of cylinder block, coaxiality error (CE) between main shaft and cylinder block, and other factors, especially eccentric wear (OTEW) of valve plate on wedge angle of the micro lubricating gap between valve plate and cylinder block, and a novel trigonometric function model of the gap geometry and mechanical balance equations of cylinder block are proposed. The three eddy current displacement sensors are used to measure the gap thickness. The results show that, the theoretical wedge angle due to FTB is nearly 1.2E-4, the test wedge angle owing to CE 1.65E-4~4.3E-4, the wedge angle by OTEW about 1.35E-3, therefore, CE and OTEW have a larger impact on the wedge angle. The test results demonstrate the total wedge angle obviously increases with the enlargement of swash plate angle but slightly rises with the increasing working pressure.

Simulation and research of one-way valve Piston Pump based on AMESim

Plunger pump is the main pressure source in high pressure hydraulic system, the inclination Angle of the swash plate in the plunger pump is one of the main factors affecting the performance and efficiency of the hydraulic system. This paper deeply analyzes the swash plate Angle and the plunger form on the influence of the plunger pump flow and pressure, theoretical analysis, numerical calculation and AMESim simulation were used to analyze and compare the flow and pressure of the plunger pump under different conditions, and the pressure flow curve of the plunger pump was obtained, which laid a foundation for the structural design and pressure flow characteristics of the plunger pump.

Research on Quasi-Synchronous Grid-Connected Control of Hydraulic Wind Turbine

The hydraulic wind turbine(HWT) is taken as the research object. To realize the quasi-synchronized safe connection of the HWT, the mathematical model of the fixed displacement pump - variable motor is first established, and the multiplicative nonlinearity existing in the modeling process is solved by the small signal linearization method. For the closed-loop speed regulation system of fixed displacement pump-variable motor, a variable speed input-constant speed output control method based on indirect flow feedback and direct-speed closed-loop system is proposed. Combining MATLAB/Simulink@ and a semi-physical simulation experiment platform of 30kVA HWT, the influence law of some parameters is analyzed for the response characteristics of the speed control system, such as the valve control cylinder response speed, the swash plate reference conversion value, initial swash plate angle and so on. At the same time, combined with the grid connection conditions for generators, a quasi-synchronized grid speed control method for HWT is proposed. Based on simulation and experimental methods, the instantaneous impact of grid connection is effectively suppressed.

Potential energy recovery scheme with variable displacement asymmetric axial piston pump

Hydraulic systems are widely used in construction machinery and equipment. However, the energy efficiency of hydraulic system is low. In many cases, hydraulic systems output energy to lift the working device. During the lowering process, the potential energy is commonly wasted through the throttling loss of the control valve. Recovering the potential energy is an efficient way to improve the hydraulic system efficiency. In this article, theoretical analysis, simulation calculation, and experimental verification were used to study the energy recovery efficiency of a differential cylinder system controlled by variable displacement asymmetric axial piston pump. Meanwhile, the influence of the load, motor speed, variable displacement asymmetric axial piston pump swashplate angle, accumulator pressure and capacity, and other key parameters on the potential energy recovery efficiency and system performance was analyzed. The results show that the system energy consumption can be reduced effectively by using the potential energy recovery system. When the load, motor speed, pre-charge pressure and capacity of the accumulator, and swashplate angle are 440 kg, 1000 r/min, 2.5 MPa, 1.6 L, and ±5°, respectively, the system’s energy-saving effect can be up to 39.25%. Considering that only the vertical motion of the differential cylinder controlled by variable displacement asymmetric axial piston pump was analyzed, in future work, the corresponding parameter optimization and control strategy will be carried out to obtain good energy recovery effect, and the influence of accumulator pre-charge pressure on the energy-saving effect will be conducted.

The development of the CS valve used to the variable swash plate compressor for a vehicle air-conditioning system

Since the variable swash plate type compressor used in the vehicle air-conditioning system is mounted on the engine and uses the power of the vehicle, many studies have been conducted on improving the performance of the compressor in order to increase the fuel efficiency of the vehicle. This study was also carried to improve compressor performance through the control room & suction muffler (CS) valve which is an on-off valve located between the control room and suction muffler. The swash plate angle can be controlled by the control room pressure adjusted with control gas. The flow of control gas starts from compressed high-pressure gas which is in the discharge muffler, flows into the control room through the external control valve (ECV) and then flows out to suction muffler through the CS hole which is located between the control room and suction muffler. Such this control method is using the compressed discharge refrigerant so that the compressor power is increased when the amount of the control gas is increased. Therefore, in this study, the CS valve has been developed to reduce the compressor power by minimizing the amount of control gas and it has been confirmed that the compressor power was reduced about 5~10% by the compressor operation speed.

Prediction on the lubrication and leakage performance of the piston–cylinder interface for axial piston pumps

Hydraulic piston pump has the advantages of high efficiency and low-pressure pulsation and has been widely used in the field of construction and agriculture machinery. However, the oil leakage problem, especially the internal leakage of the piston, seriously affects the efficiency of the pump and causes unstable state and high noise. First of all, to improve the performance of the hydraulic pump, a nonlinear mathematical model of the Reynolds equation and energy equation was established to predict the oil film thickness and pressure distribution. What's more, the influence of multiple parameters such as pressure, temperature, swash plate angle, leakage clearance, and the length of leakage flow path on the internal leakage of the piston–cylinder interface was explored. Last but not the least, a test rig was built to measure the corresponding values and to evaluate the effectiveness of the mathematic model. Simulations and experiments consider the variables such as pressure, temperature, and swash plate angle. Both results show that the nonlinear mathematical model could predict the piston pair leakage accurately, so it could be an effective way to improve the design of the piston–cylinder surface structure, gaining higher efficiency.

The influence of dynamic swash plate vibration on outlet flow ripple in constant power variable-displacement piston pump

The vibration of a swash plate is caused by the piston forces and the control actuator acting on the swash plate. An earlier study of the outlet flow ripple of variable-displacement axial piston pumps assumed a fixed swash plate angle; it ignored the influence of swash plate vibration on the outlet flow ripple of the axial piston pump. In this work, a theoretical model of the outlet flow ripple and pressure pulsation was established in a constant power variable-displacement piston pump. The vibration of swash plate, flow leakage, and valve dynamic characteristics are considered in the theoretical model. The computational results of the theoretical model at different external load pressures are verified by comparison with experimental results. The vibration of the swash plate is strongly influenced by both the piston chamber pressure variation and the control actuator mechanism. The study proved the influence of the swash plate vibration on the outlet flow ripple and the pressure pulsation of an axial piston pump. Compared to the case of a fixed swash plate angle, accounting for swash plate vibration is much more suitable for the accurate determination of the outlet flow ripple and pressure pulsation of an axial piston pump. It is also shown that the vibration of the swash plate affects the valve plate design. Accordingly, valve plate optimization based on the theoretical model of the outlet flow ripple was also studied in this work. The amplitude of the instantaneous outlet flow ripple was considered as the optimization objective function. Finally, the optimized design parameters for a constant power variable-displacement swash plate axial piston pump were evaluated.

Active Power Control of Hydraulic Wind Turbines during Low Voltage Ride-Through (LVRT) Based on Hierarchical Control

To improve the power grid adaptability and low voltage ride-through (LVRT) capability of hydraulic wind turbines (HWT), an LVRT control method based on hierarchical control is proposed for the energy regulation of HWT. The method includes a top-level machine-controlled paddle, mid-level control based on variable motor swash plate angle, and an underlying control based on throttle opening. To achieve multivariable coordinated control of the HWT via the control process, the minimum wind, maximum inertial energy storage, and minimum energy consumption of the throttle valve of the wind turbine are optimized. The multiobjective control law is computed by a quadratic programming algorithm, and the optimal control law is obtained. The multitarget control strategy is simulated and analyzed by AMESim14 and MATLAB/Simulink R2014a software, and the control law is verified by a semiphysical test platform of an HWT. The results show that the proposed control method can effectively reduce the residual energy of the HWT during LVRT, reduce the impact on the generator, and improve the adaptability of the HWT.

Variable load failure mechanism for high-speed load sensing electro-hydrostatic actuator pump of aircraft

This paper presents a novel transient lubrication model for the analysis of the variable load failure mechanism of high-speed pump used in Load Sensing Electro-Hydrostatic Actuator (LS-EHA). Focusing on the slipper/swashplate pair partial abrasion, which is considered as the dominant failure mode in the high-speed condition, slipper dynamic models are established. A forth sliding motion of the slipper on the swashplate surface is presented under the fact that the slipper center of mass will rotate around the center of piston ball when the swashplate angle is dynamically adjusted. Besides, extra inertial tilting moments will be produced for the slipper based on the theorem on translation of force, which will increase rapidly when LS-EHA pump operates under high-speed condition. Then, a dynamic lubricating model coupling with fluid film thickness field, temperature field and pressure field is proposed. The deformation effects caused by thermal deflection and hydrostatic pressure are considered. A numerical simulation model is established to validate the effectiveness and accuracy of the proposed model. Finally, based on the load spectrum of aircraft flight profile, the variable load conditions and the oil film characteristics are analyzed, and series of variable load rules of oil film thickness with variable speed/variable pressure/variable displacement are concluded.

Simulation of parameters of hydraulic drive with volumetric type controller

The article presents a mathematical model of volumetric type hydraulic drive controller that allows to calculate the parameters of forward and reverse motion. According to the results of simulation static characteristics of rod’s speed and the force of the hydraulic cylinder rod were built and the influence of the angle of swash plate of the controller at the characteristics profile is shown. The results analysis showed that the proposed controller allows steplessly adjust the speed□ц of hydraulic cylinder’s rod motion and the force developed on the rod without the use of flow throttling.

Fault diagnosis of an intelligent hydraulic pump based on a nonlinear unknown input observer

Hydraulic piston pumps are commonly used in aircraft. In order to improve the viability of aircraft and energy efficiency, intelligent variable pressure pump systems have been used in aircraft hydraulic systems more and more widely. Efficient fault diagnosis plays an important role in improving the reliability and performance of hydraulic systems. In this paper, a fault diagnosis method of an intelligent hydraulic pump system (IHPS) based on a nonlinear unknown input observer (NUIO) is proposed. Different from factors of a full-order Luenberger-type unknown input observer, nonlinear factors of the IHPS are considered in the NUIO. Firstly, a new type of intelligent pump is presented, the mathematical model of which is established to describe the IHPS. Taking into account the real-time requirements of the IHPS and the special structure of the pump, the mechanism of the intelligent pump and failure modes are analyzed and two typical failure modes are obtained. Furthermore, a NUIO of the IHPS is performed based on the output pressure and swashplate angle signals. With the residual error signals produced by the NUIO, online intelligent pump failure occurring in real-time can be detected. Lastly, through analysis and simulation, it is confirmed that this diagnostic method could accurately diagnose and isolate those typical failure modes of the nonlinear IHPS. The method proposed in this paper is of great significance in improving the reliability of the IHPS.

Nonlinear Model Predictive Control of Axial Piston Pumps

Variable displacement axial piston units are the core components of many hydrostatic and hydraulic hybrid drive trains. Therein, the fast and accurate control of the swash plate angle, utilizing the full possible dynamics of the displacement system, is essential for a good performance of the overall drive train. This paper describes the development, implementation, and the experimental validation of a control strategy for the swash plate angle based on nonlinear model predictive control (NMPC). A tailored mathematical model, which serves as the basis for the NMPC, is described in the first part of the paper. Two versions of NMPC, an indirect and a direct method, are compared with respect to their numerical complexity and their capability of handling input and state constraints. An observer strategy, which is designed to obtain the nonmeasurable states and varying parameters of the system, completes the overall control strategy. To reduce the negative influence of stick–slip friction, the concept of dithering is applied in the experimental implementation. The differences of the NMPC methods are analyzed by simulation studies and experiments. Finally, the experimental results, using an industrial electronic control unit (ECU), prove the practical feasibility and the improved control accuracy and robustness in comparison to classical (nonlinear) control strategies.