Axial Piston Pump Research Articles

One-Dimensional Fluid Dynamic Modeling of a Gas Bladder Hydraulic Damper for Pump Flow Pulsation

Positive displacement pumps produce pressure ripple that can be reduced with the attenuation of the generated flow ripple. This paper presents the application of a gas bladder hydraulic damper with the aim of reducing the oscillations of the delivery flow rate of positive displacement machines. This work is focused on the development of a 1D fluid dynamic model of the damper, which is based on the fundamental fluid motion equations applied for a mono-dimensional flow. In order to represent the fluid flow inside the damper, a particular evaluation of the sound speed has been implemented. Experimental tests have been performed involving an axial piston pump with the damper installed in the delivery pipe to validate the model; tests were carried out at different pump working conditions and with different gas precharge pressure of the damper. The test results confirmed the effectiveness of the device, and the comparison with numerical results demonstrated a good agreement. Simulations have been carried out to investigate the influence of various parameters on damper effectiveness.

A Computer-Aided Intelligent Fault Diagnosis Method for Axial Hydraulic Piston Pump

<p>Axial hydraulic piston pump is widely used in industrial production due to its high pressure resistance and large displacement characteristics, but high pressure and large displacement are also the main causes of piston pump failure. Starting from the fault mechanism of the axial hydraulic piston pump, this paper analyzes and studies the signal characteristics of the fault, and establishes the fault signal acquisition and analysis model. Finally, it discusses the construction of the diagnosis system from both hardware and software, so that the processed typical fault signals can be sent into the intelligent diagnosis system to determine the fault type. Finally, the method in this paper is verified by experiments, which proves the reliability and effectiveness of the diagnosis system.</p> <p> </p>

The Difference in Tribological Characteristics between CFRPEEK and Stainless Steel under Water Lubrication in Friction Testing Machine and Axial Piston Pump

A water lubricating axial piston pump (WLPP) is the core power component of a green and environmentally friendly water hydraulic system. The friction and wear of the friction pairs of a WLPP are the key factors that restrict its development. In order to explore the friction and wear mechanism of materials, the tribological properties of CFRPEEK against 316L and 1Cr17Ni2 under water lubrication were investigated in a friction testing machine and an axial piston pump, respectively. An environmental scanning electron microscope (ESEM), confocal laser scanning microscopy and a surface profiler were used to analyze the morphology of the samples. In a friction testing machine, two different metals are paired with CFRPEEK, and the friction coefficient and wear rate barely show any differences. The wear rate of CFRPEEK is two orders of magnitude higher than that of metal. In the WLPP, 316L can hardly be paired with CFRPEEK, while 1Cr17Ni2 works well. The wear of 1Cr17Ni2 in the WLPP is greater than that of CFRPEEK. The high-pressure water film lubrication friction pairs cause the wear of the metal and show the difference in these two test methods. The wear mechanism is mainly abrasive wear. Improving the wear resistance of metals is very important for the development of WLPP.

Predictive Diagnosis in Axial Piston Pumps

Increasing reliability, availability and safety requirements as well as an increasing amount of data acquisition systems have enabled condition-based maintenance in mobile and industrial machinery. In this paper, we present a methodology to develop a robust diagnostic approach. This includes the consideration of variable operating conditions in the data acquisition process as well as a versatile, non domain-specific feature extraction technique. By doing so, we train anomaly detection models for different fault types and different fault intensities in variable displacement axial piston pumps. Our specific interest points to the investigation of high-frequency condition indicators with a sampling rate of 1 MHz. Furthermore, we compare those to industry standard sensors, sampled with up to 20 kHz.By considering variable operating conditions, we are able to quantify the influence of the operating point. The results show, that high-frequency features are a suitable condition-indicator across several operating points and can be used to detect faults more easily. Although set up on a test-bench, the experimental design allows to draw conclusions about realistic field operational conditions.

Quasi-periodic Inspection and Preventive Maintenance Policy Optimisation for a system with Wiener Process degradation

Periodic inspection policy is performed for some degradation systems to check their degradation states, whereas it is usually difficult to implement on time due to impact of some random factors. Inspections and some maintenance actions are implemented in an inspection window with random, and thus how to optimize the inspection windows and the degradation threshold of the system to perform preventive maintenance (PM) are beneficial in practice. To this end, an optimisation of quasiperiodic inspection and PM policy with inspection window is proposed for a degradation system whose degradation followed Wiener process with a linear drift. Assume that PM can change the degradation rate and inspections are randomly performed in each inspection window. After optimisation, the optimal interval of the inspection window, the degradation threshold of PM and PM policy are determined by minimising the long-term running cost rate of the system. Finally, modeling and optimisation are illustrated using the degradation process of an axial piston pump, and the sensitivity analysis of some key parameters is conducted.

Failure Analysis and Intelligent Identification of Critical Friction Pairs of an Axial Piston Pump

Hydraulic axial piston pumps are the power source of fluid power systems and have important applications in many fields. They have a compact structure, high efficiency, large transmission power, and excellent flow variable performance. However, the crucial components of pumps easily suffer from different faults. It is therefore important to investigate a precise fault identification method to maintain reliability of the system. The use of deep models in feature learning, data mining, automatic identification, and classification has led to the development of novel fault diagnosis methods. In this research, typical faults and wears of the important friction pairs of piston pumps were analyzed. Different working conditions were considered by monitoring outlet pressure signals. To overcome the low efficiency and time-consuming nature of traditional manual parameter tuning, the Bayesian algorithm was introduced for adaptive optimization of an established deep learning model. The proposed method can explore potential fault feature information from the signals and adaptively identify the main fault types. The average diagnostic accuracy was found to reach up to 100%, indicating the ability of the method to detect typical faults of axial piston pumps with high precision.

Characteristics of Various Losses of Axial Piston Pump and Bent Axis Hydro-motor with respect to Displacement Conditions and Load Demands

The hydrostatic transmission is one of the most important applications in the fluid power systems. It gives smooth change in output speed, torque and power as per the design requirements. Present article deals with various losses of the hydraulic pump and motor using a closed circuit hydraulic drive. The drive basically consists of a variable displacement axial piston pump that supplies pressurized fluid to a variable displacement bent axis hydro-motor. In investigating the pump/motor performance, bond graph simulation technique is used to model the drive system. Various losses of the pump and motor are accounted in the model by suitable resistive elements. The characteristics of them are identified through experiments. The predicted performance of the pump/motor is studied with respect to the displacement and load at the same time they are validated experimentally. The investigation made in the article identifies the control strategy which will be useful for the practicing engineers to select best combination of the pump and motor displacement for optimizing the drive performance and minimizing the losses as well. The study performed in this research work will be useful for the similar hydraulic configuration used in mobile equipment.

A Novel Fault Diagnosis Method Based on SWT and VGG-LSTM Model for Hydraulic Axial Piston Pump

Since the hydraulic axial piston pump is the engine that drives hydraulic transmission systems, it is widely utilized in aerospace, marine equipment, civil engineering, and mechanical engineering. Operating safely and dependably is crucial, and failure poses a major risk. Hydraulic axial piston pump malfunctions are characterized by internal concealment, challenging self-adaptive feature extraction, and blatant timing of fault signals. By completely integrating the time-frequency feature conversion capability of synchrosqueezing wavelet transform (SWT), the feature extraction capability of VGG11, as well as the feature memory capability of the long short-term memory (LSTM) model, a novel intelligent fault identification method is proposed in this paper. First, the status data are transformed into two dimensions in terms of time and frequency by using SWT. Second, the depth features of the time–frequency map are obtained and dimensionality reduction is carried out by using the deep feature mining capability of VGG11. Third, LSTM is added to provide the damage identification model for long-term memory capabilities. The Softmax layer is utilized for the intelligent evaluation of various damage patterns and health state. The proposed method is utilized to identify and diagnose five typical states, including normal state, swash plate wear, sliding slipper wear, loose slipper, and center spring failure, based on the externally observed vibration signals of a hydraulic axial piston pump. The results indicate that the average test accuracy for five typical state signals reaches 99.43%, the standard deviation is 0.0011, and the average test duration is 2.675 s. The integrated model exhibits improved all-around performance when compared to LSTM, LeNet-5, AlexNet, VGG11, and other typical models. The proposed method is validated to be efficient and accurate for the intelligent identification of common defects of hydraulic axial piston pumps.

Effect of Composite Bionic Micro-Texture on Bearing Lubrication and Cavitation Characteristics of Slipper Pair

The slipper pair is the crucial friction pair of the seawater axial piston pump. Taking seawater as the working medium will inevitably affect the bearing performance of the slipper pair. In this paper, a seawater axial piston pump slipper pair model with a composite bionic micro-texture of the first-stage circular pit and the second-stage circular ball is established. Using the CFD simulation method, 18 groups of orthogonal tests are designed to explore the effects of seven test factors, such as rotational speed, first-stage diameter, first-stage aspect ratio, second-stage diameter, second-stage aspect ratio, area ratio, and distribution angle, on the bearing characteristics of the water film of the slipper pair. Study whether cavitation can further improve the bearing characteristics of the water film. The research shows that there is a vortex behind the circular pit, and there is a pressure difference in the calculation domain of the water film. The existence of the pressure difference causes the bearing force of the water film surface to increase. The cavitation phenomenon mainly occurs at the divergent wedge behind the circular pit. Among them, the total pressure bearing force of the 5th test group increased by 90% after introducing cavitation effect, and the total pressure bearing force of the 17th test group increased by about 86% compared with other test groups at the same speed. The order of the test factors affecting the water film bearing features is: A (rotational speed) > C (first-stage aspect ratio) > B (first-stage diameter) > E (second-stage aspect ratio) > F (area ratio) > D (second-stage diameter) > G (distribution angle). The optimal model is A6B2C1D3E3F2G3.

Rapid Prototyping of H∞ Algorithm for Real-Time Displacement Volume Control of Axial Piston Pumps

A system for the rapid prototyping of real-time control algorithms for open-circuit variable displacement axial-piston pumps is presented. In order to establish real-time control, and communication and synchronization with the programmable logic controller of an axial piston pump, the custom CAN communication protocol is developed. This protocol is realized as a Simulink® S-function, which is a part of main Simulink® model. This model works in real-time and allows for the implementation of rapid prototyping of various control strategies including advanced algorithms such as H∞ control. The aim of the algorithm is to achieve control system performance in the presence of various load disturbances with an admissible control signal rate and amplitude. In contrast to conventional systems, the developed solution suggests using an embedded approach for the prototyping of various algorithms. The obtained results show the advantages of the designed H∞ controller that ensure the robustness of a closed-loop system in the presence of significant load disturbances. These type of systems with displacement volume regulation are important for industrial hydraulic drive systems with relatively high power.

Modellversuch für die experimentelle Untersuchung des Verschleißverhaltens des Gleitschuh-Schrägscheibe Kontakts

In axial piston pumps, hydrostatically partially balanced contacts are predominantly used. The use of these pumps in variable-speed configurations, such as in electro-hydrostatic axes, has proven to be very challenging in terms of robustness. Particularly affected here is the slipper-swashplate contact, via which the piston loads are supported. The wear processes and driving effects occurring here have not yet been sufficiently addressed in the current state of research. Within the scope of this publication, a model experiment is therefore to be presented which allows the targeted investigation of the wear behaviour of the slipper-swashplate contact under controlled and reproducible conditions. The objectives of the model experiment are, on the one hand, the empirical investigation of the interactions in variable-speed operation and, on the other hand, the validation of simulative considerations.

Simulation Study on Bearing Lubrication Mechanism and Friction Characteristics of the Biomimetic Non-Smooth Surface of a Cross-Scale, Second-Order Compound Microstructure

The reasonable design of biomimetic non-smooth surfaces is a novel and effective way to solve problems such as the poor lubricity and serious friction and wear of friction pairs of seawater axial piston pumps. Inspired by cross-scale, second-order compound microstructures on the surfaces of some living organisms, a hydrodynamic lubrication model of a slipper pair with a surface featuring spherical pits containing spherical convex hulls was built. This study analyzed the bearing lubrication mechanism and friction characteristics of cross-scale, second-order compound microstructure from the microflow perspective via the CFD method and optimized the working and geometric parameters using a hybrid orthogonal test scheme. The study’s results show that the cross-scale, second-order compound microstructure can produce a superimposed hydrodynamic pressure effect to improve the bearing capacity of the lubrication film of a slipper pair, reducing the friction coefficient. The orders of factors (the working parameter and geometric parameters) under multiple indices (the total pressure-bearing capacity and the friction coefficient) were found. The optimal combination is a spherical pit with a first order diameter of 0.7 mm, a first order depth-to-diameter ratio of 0.1, an area rate of 20%, an arrangement angle of α/3 and a spherical convex hull with a second order diameter of 0.13 mm, and a second order depth-to-diameter ratio of 0.3. Compared to a smooth surface and a first-order, non-smooth microstructure, the cross-scale, second-order compound microstructure has an 11.0% and 8.9% higher total pressure-bearing capacity, respectively, and the friction coefficient decreased by 9.5% and 5.4%, respectively.

Numerical simulation on hydrodynamic lubrication performance of bionic multi-scale composite textures inspired by surface patterns of subcrenata and clam shells

Inspired by the surface of shells in natural world, six bionic multi-scale composite surface textures were designed. Numerical simulation was carried out to investigate the mechanism for influences of the texture geometric parameters and service conditions on lubrication characteristics. The results revealed that the bionic surface enhanced the load-carrying capacity and reduced the friction coefficient. Groove combinations offered a better lubrication performance than wavy combinations. The texture geometric parameters showed significant influence on the frictional characteristics. For all texture shapes, the load-carrying capacity increased approximately linearly with the rotational speed and decreased with the water film thickness. The results would help guide effective texture design to improve the lubrication performance of axial piston pump friction pairs under marine environments.

Distribution Mechanism of Asymmetric Axial Piston Pump

Pump-controlled single-rod hydraulic cylinders are energy-saving and efficient, which is the development direction of hydraulic systems in the future. However, the flow imbalance caused by the unequal effective areas of the two chambers of single-rod hydraulic cylinders has always restricted the development and application of pump-controlled single-rod hydraulic cylinders. The flow rate of the inlet and outlet ports of the ordinary axial piston pump is equal and the flow rate of the large and small chambers of the single rod hydraulic cylinder does not match. In order to solve this problem, the ordinary axial piston pump is improved into an asymmetric axial piston pump, on this basis, the flow distribution mechanism of the asymmetric axial piston pump is explored, and the design theory of the asymmetric axial piston pump is improved. Theoretical analysis of the relationship between the angle of the distribution window of the asymmetrical axial piston pump and the area ratio of the single-rod hydraulic cylinder is carried out, and its mathematical model is derived. Design of valve plates for asymmetrical axial piston pumps to match single rod hydraulic cylinders with different area ratios. The physical model of the asymmetrical axial piston pump and the asymmetrical axial piston pump controlled single-rod hydraulic cylinder system was established in the computer simulation software AMESim. The simulation analysis of the inlet and outlet flow of the asymmetric axial piston pump under different working conditions and the matching of the asymmetric axial piston pump and the single-rod hydraulic cylinder with different area ratios. The simulation results show that the use of an asymmetrical axial piston pump can compensate the flow imbalance caused by the unequal effective areas of the two chambers of the single-rod hydraulic cylinder, so that the flow of the asymmetrical axial piston pump and the single-rod hydraulic cylinder can completely match.

New analytical leakage models for tribological interfaces in axial piston pumps

Axial piston pumps act as the power source in hydraulic systems and their volumetric losses mainly arise from leakage of tribological interfaces. The leakage of tribological interfaces was often modeled as a simple mixture of pressure-induced flow and velocity-induced flow in previous studies. However, few studies have clarified the contribution of discharge pressure and rotational speed to the leakage flow. This work considers both pressure and velocity factors and establishes new analytical models for the leakage of tribological interfaces from Navier-Stokes equations. Experiments were performed on an actual axial piston pump to measure its leakage flow rates at different discharge pressures and rotational speeds. Results show that the total pump leakage excludes Couette flow and only includes Poiseuille and centrifugal flows. The Poiseuille flow predominates the pump leakage while the centrifugal flow contributes little to the pump leakage.

Performance optimization for high speed axial piston pump considering cylinder block tilt

Increasing the rotating speed is considered as an efficient approach to upgrade the power-to-weight ratio in an axial piston pump, but penalized by more leakage and more severe wear resulting from the adverse cylinder block tilt. Previous studies mainly focused on the bearing characteristic of the valve plate/cylinder block pair, but the spline coupling also plays a key role in the undesired cylinder block tilt, which has been little studied. A theoretical model for the rotating assembly is presented to investigate the effect of the spline coupling length on the cylinder block tilt and the performance of the valve plate/cylinder block pair. A typical high-speed axial piston pump with the displacement of 5.2 mL/r at 10000 r/min was studied by simulation and experiment. It shows that the optimal spline coupling length is one value increased by 2 mm from the original, bringing a remarkable leakage reduction under the high-speed condition by decreasing the cylinder block tilting angle. The experiment result matches well with the simulation. The influences of the spline coupling on the cylinder block tilt and the leakage were demonstrated.

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.

Classification of Wear State for a Positive Displacement Pump Using Deep Machine Learning

Hydraulic power systems are commonly used in heavy industry (usually highly energy-intensive) and are often associated with high power losses. Designing a suitable system to allow an early assessment of the wear conditions of components in a hydraulic system (e.g., an axial piston pump) can effectively contribute to reducing energy losses during use. This paper presents the application of a deep machine learning system to determine the efficiency state of a multi-piston positive displacement pump. Such pumps are significant in high-power hydraulic systems. The correct operation of the entire hydraulic system often depends on its proper functioning. The wear and tear of individual pump components usually leads to a decrease in the pump’s operating pressure and volumetric losses, subsequently resulting in a decrease in overall pump efficiency and increases in vibration and pump noise. This in turn leads to an increase in energy losses throughout the hydraulic system, which releases excess heat. Typical failures of the discussed pumps and their causes are described after reviewing current research work using deep machine learning. Next, the test bench on which the diagnostic experiment was conducted and the selected operating signals that were recorded are described. The measured signals were subjected to a time–frequency analysis, and their features, calculated in terms of the time and frequency domains, underwent a significance ranking using the minimum redundancy maximum relevance (MRMR) algorithm. The next step was to design a neural network structure to classify the wear state of the pump and to test and evaluate the effectiveness of the network’s recognition of the pump’s condition. The whole study was summarized with conclusions.

Development of entropy measure for selecting highly sensitive WPT band to identify defective components of an axial piston pump

This paper proposes a novel tangent hyperbolic fuzzy entropy measure-based method for determining the highly (most) sensitive frequency band to easily identify defective components in an axial piston pump. The validation of proposed scheme was done by experimental and simulation analysis. In the proposed method, initially, the raw vibration signal is decomposed into 16 frequency bands. Second, the energy of the WPT band is computed. Third, lower bounds of energy readings at the 4th level of decomposition are extracted, and thereafter they are normalised and finally converted into the forms of fuzzy sets. Following that, the proposed measure's value is computed. The proposed measure is analogous to the quantity of available information. The WPT4 band with the highest measure value will have the most information and can be designated as sensitive. Finally, envelope demodulation of the sensitive band is computed to identify the defects by evaluating the magnitude of vibration at fundamental frequencies. The superiority of the proposed sensitive band selection technique has been justified by comparing the findings with the widely used Fast-Kurtogram, Protugram, and Spectral-Kurtosis methods. The authenticity of the proclaimed tangent hyperbolic fuzzy entropy measure is accomplished with the existing Deluca and Termini fuzzy entropy measures. The latter entropy measure exhibited some inconsequential and unspecified results and established the superiority of our defect identification methodology.

Failure analysis of auxiliary support bearing/shaft tribopair in seawater hydraulic axial piston pump

The auxiliary support structure is used to prevent the cylinder block from tilting in seawater hydraulic axial piston pump (SHAPP). The failure modes of auxiliary support bearing and shaft under different material combinations were compared. Experimental results show that improper design of radius fitting clearance in auxiliary support bearing/shaft tribopair will seriously affect the normal operation of SHAPP and even lead to its damage. Based on the inertia force, nonlinear water film force and dynamic load balance of the rotating cylinder block, the mathematical model of the nonlinear shaft centerline orbit of the auxiliary support bearing was established. The nonlinear shaft centerline orbit of auxiliary support bearing in the cylinder block bore during SHAPP operation is analyzed accurately. Simultaneously, the water film pressure field under different radius fitting clearance is simulated and the range of the optimal value is determined. The running-in experiment of SHAPP is carried out under the optimum clearance of the auxiliary support bearing/shaft tribopair. The results show that the SHAPP can run normally and the performance is obviously improved without the wear on the friction pair surfaces. Therefore, the proposed method has provided the guidance reference for the design of auxiliary support bearing in SHAPP.