Hydraulic Piston Pump Research Articles

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.

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.

Dynamic Response of a Digital Displacement Motor Operating with Various Displacement Strategies

Digital displacement technology has the potential of revolutionizing the performance of hydraulic piston pumps and motors. Instead of connecting each cylinder chamber to high and low pressure in conjunction with the shaft position, two electrically-controlled on/off valves are connected to each chamber. This allows for individual cylinder chamber control. Variable displacement can be achieved by using different displacement strategies, like for example the full stroke, partial stroke, or sequential partial stroke displacement strategy. Each displacement strategy has its transient and steady-state characteristics. This paper provides a detailed simulation analysis of the transient and steady-state response of a digital displacement motor running with various displacement strategies. The non-linear digital displacement motor model is verified by experimental work on a radial piston motor.

Study on the influence of rubber isolator's dynamic stiffness on the dynamic behavior of seawater hydraulic piston pump

Rubber isolator is commonly used as vibration isolation device for piston pump, and the vibration of piston pump can be effectively reduced by adjusting the dynamic stiffness of rubber isolator. In this paper, in order to study the effect of rubber isolator's dynamic stiffness on the dynamic of seawater hydraulic piston pump (SWHPP), four kinds of rubber isolators with different dynamic stiffness were selected. An experimental modal analysis (EMA) experiment was conducted to study the influence of rubber isolator's dynamic stiffness on the natural frequency of SWHPP. The experimental results indicated that the natural frequency of the pump structure decreased as the dynamic stiffness of rubber isolator increased. Then, the influence of the rubber isolator's dynamic stiffness on the vibration of SWHPP was further studied, and conclusions can be obtained that: the vibration level of the pump decreases with the dynamic stiffness of rubber isolator increases. For the four kinds of rubber isolators, when the dynamic stiffness of rubber isolator is 5800N/cm, the vibration reduction effect of the isolator is the best, which reaching 38%. In addition, the dynamic stiffness of rubber isolator mainly affects the vibration of the pump in the frequency of 0–20 Hz.

A Vibration Signal-Based Method for Fault Identification and Classification in Hydraulic Axial Piston Pumps

In recent years, the interest of industry towards condition-based maintenance, substituting traditional time-based maintenance, is growing. Indeed, condition-based maintenance can increase the system uptime with a consequent economic advantage. In this paper, a solution to detect the health state of a variable displacement axial-piston pump based on vibration signals is proposed. The pump was tested on the test bench in different operating points, both in healthy and faulty conditions, the latter obtained by assembling damaged components in the pump. The vibration signals were acquired and exploited to extract features for fault identification. After the extraction, the obtained features were reduced to decrease the computational effort and used to train different types of classifiers. The classification algorithm that presents the greater accuracy with reduced features was identified. The analysis has also showed that using the time sampling raw signal, a satisfying accuracy could be obtained, which will permit onboard implementation. Results have shown the capability of the algorithm to identify which fault occurred in the system (fault identification) for each working condition. In future works, the classification algorithm will be implemented onboard to validate its effectiveness for the online identification of the typical incipient faults in axial-piston pumps.

Опыт апробации гидропоршневых насосных установок в скважинах месторождения Белый Тигр

Опыт апробации гидропоршневых насосных установок в скважинах месторождения Белый Тигр

Design of the Hydrostatic Thrust Spherical Bearing with Restrictors (Fitted Type)

The hydrostatic bearings are broadly observed in industrial applications owing to their potential characteristics of low running friction, high load-carrying capacity, high stiffness and small viscous dissipation. Spherical bearings have advantages over other configurations of bearings because of their self-aligning property and also their capacity to accept both radial and thrust loads. Operation of the spherical bearings is unaffected by angular miss-alignment. They are mainly used in machine tools, precision measuring instruments, hydraulic piston pumps and motors, gyroscope gimbals, telescopes, radar tracking units, air craft engines and rotary drum of centrifugal separator for enriched uranium. The main objective of this part of study is to handle the fitted bearing design taking into consideration the combined effects of rotational inertia, surface roughness and the fluid film viscosity variability. The mathematical expressions derived in part 2 for this type of bearings with its different configurations (with and without recess; hemispherical and partial hemispherical seats) have been used in the detailed bearing design. Improving the previous design through developing some mathematical expressions, a new conception is adopted to reveal the bearing consistency showing how the fluid flow rate pulsation or intermittent could be prevented. The detailed design procedures show the advantages of this method to get the central pressure ratio mathematically through maximizing the flow rate with minimizing the supply pressure which means minimum pump power to get maximum discharge. This design showed very high mean static stiffness of all the bearing configurations and an acceptable temperature rise for a heavy duty bearing without the need to a use a cooling system.

Piston surface design to improve the lubrication performance of a swash plate pump

Abstract Mechanical power loss in hydraulic piston pumps comes from the friction between parts in relative motion, and wear is among the top pump failure mechanisms. Reducing friction and preventing wear require lubrication enhancement, which may be accomplished by proper surface texture design. Cylinder length is an important factor affecting the lubrication performance of the piston-cylinder system in a swash-plate pump. Our previous analyses revealed that under the same load, increasing the cylinder length could decrease the maximum pressure and increase the minimum film thickness, favorable for the pump operation with reduced wear; however, friction would become higher. The work reported in this paper intends to lower friction by textures in the piston surface while increasing, or at least maintaining, the load capacity of the piston system. Several textures are designed and their lubrication performances investigated, aiming at reducing the piston friction and improving the load-carrying ability of the system in a wide range of operation conditions. The effects of texture type, application location, and texture shape are studied, and their relationships with the friction and film thickness characteristics of the piston-cylinder interface are explored. Two optimal surface-texture designs are suggested, which are named the Step-Multiple-Grooves design and the Combine design.

Numerical simulation and analysis of temperature and flow field of high‐speed axial piston motor pump

Based on the theories of heat transfer and the method of computational fluid dynamics, a liquid–solid mathematical model of heat transfer of an axial piston hydraulic motor pump is constructed in this study. Through the finite volume method, the model with different cooling runners has been solved. Meanwhile, the oil flow regularity of runner and temperature distribution of the motor pump and oil duct has been obtained. On the basis of the model of long-strip runner, the influence of ambient temperature on the motor pump's temperature rise has been analysed. The result shows that the cooling channels on the housing of the hydraulic motor pump effectively reduce the temperature rise, and a long-strip channel is for optimum cooling. The average temperature rise of the motor pump increases linearly with the increase of ambient temperature.

Comparative evaluation on friction and wear characteristics of SiC, Si 3 N 4 , Al 2 O 3 , and ZrO 2 sliding against PEEK composite for seawater hydraulic axial piston pumps

Comparative investigation on friction and wear properties of SiC, Si3N4, Al2O3, and ZrO2 lubricated with seawater was carried out on a ring-on-ring contacted tribological test apparatus, and their worn surfaces were observed by an ultra-depth optical microscope. The results reveal that the friction coefficients of Si3N4 and SiC are obviously lower than those of Al2O3 and ZrO2 when they slide against the polyetheretherketone (PEEK) composite in seawater, and the friction stability of ZrO2 is so poor that it is not suitable for seawater hydraulic piston pumps. When the contacted load increases from 400 to 1000 N, the wear rate of Al2O3 is still the highest, while the wear rates of SiC and Si3N4 change from positive to negative, which indicates that plastic transfer is occurred under a heavier load. When they slide against the PEEK in seawater, the main tribological mechanism of SiC, Si3N4, and Al2O3 is slightly abrasive wear, while both abrasive wear and adhesive wear occur for ZrO2. Generally, both SiC and Si3N4 have wide prospect applied in seawater hydraulic piston pumps, and particularly Si3N4 exhibits excellent friction and wear properties in seawater.

Research on the Dynamics and Variable Characteristics of a Double-Swash-Plate Hydraulic Axial Piston Pump With Port Valves

Axial piston pumps with port valves are widely used in applications that require high pressure and high power. In the present research, a new type of double-swash-plate hydraulic axial piston pump (DSPHAPP) with port valves is presented. The structure and working principle of the pump are discussed, and the balance characteristics of the pump are analyzed. A mathematical model of the pump flow distribution mechanism considering the leakage is established, based on which the effects of centrifugal forces acting on the port valves, working pressure, and rotational speed on the flow distribution characteristics are studied. A new method of varying the displacement of the pump that changes the phase relation of the two swash plates is proposed, and the principle and regulating characteristics of the variable method are studied. A detailed analysis of the forces and moments acting on the cylinder and the bearing reaction forces is presented. Finally, the relationship between volumetric efficiency and working pressure, and rotational speed and variable angle, is presented. It is revealed through an analysis that the working principle of the pump is feasible, and that the variable method can meet the requirements of varying the displacement of the pump. The characteristics of static balance and dynamic balance of the double-swashplate pump have the advantage of reducing vibration and noise. The research results also show that the reasonable matching of the working pressure and rotational speed can increase the pump's working performance to its optimum level.

A Load Sequence Design Method for Hydraulic Piston Pump Based on Time-Related Markov Matrix

Accelerated life test (ALT) is commonly used to assess lifetime of mission critical and expensive products. Accurate ALT requires realistic load sequence representative of the actual and/or expected work conditions. A novel method, using the Markov information matrix, is proposed in this paper to produce the load sequence to be applied in the ALT. The proposed method provides several advantages, including improved efficiency as well as capturing dynamic characteristics of the loading conditions, such as transition frequency and cumulative time effect of the load. This paper presents the Markov method for analyzing the load sequence, in which the Markov information matrix is modified by taking into account the cumulative effect of each load level. The model is then applied to the ALT of hydraulic piston pumps, which are widely used in aircraft, in order to perform analysis of the cumulative damage. Considering the actual aircraft operation, hidden Markov model is used to generate the equivalent accelerated load sequence of a pump. The load sequence can be easily applied on a test bench for the verification and approval of pumps. Finally, an accelerated sequence design method is proposed to guide the ALT. The method ensures the consistency of the transfer frequency and the cumulative damage caused by the load, which provides an equivalent sequence for the ALT.

Dynamic modelling of the swash plate of a hydraulic axial piston pump for condition monitoring applications

In the last years Prognostic and Health Management (PHM) has become one of the challenging topic in the engineering field. In particular, model-based approach for diagnostic relies on the development of a mathematical model of the system representing its flawless status. Once the model has been developed and carefully calibrated on experimental data referred to flawless pump condition the comparison between the model output and the real system output leads to the residual analysis, which gives a diagnosis of the component health. This paper presents the mathematical model of a hydraulic axial piston pump developed in order to replicate the dynamic behavior of the swash plate for PHM applications. The model has been developed on the basis of simplified hypotheses, a friction model between swash plate and bearings has been introduced. A detailed experimental activity was carried out to calibrate and validate the model with step tests and sweep tests. The comparison between numerical and experimental results shows a satisfying agreement and highlights the model capability to reproduce the swash plate dynamics. Future works will include tests with the pump in faulty conditions to evaluate the pump health state through the residual analysis of the swash plate position.

A Methodology Based on Cyclostationary Analysis for Fault Detection of Hydraulic Axial Piston Pumps

Condition monitoring has been an active area of research in many industrial fields during the last decades, particularly in fluid power systems. This paper presents a solution for the fault diagnosis of a variable displacement axial-piston pump, which is a critical component in many hydraulic systems. The proposed methodology follows a data-driven approach including data acquisition and feature extraction and is based on the analysis of acceleration signals through the theory of cyclostationarity. An experimental campaign was carried out on a laboratory test bench with the pump in the flawless state and in faulty states. Different operating conditions were considered and each test was repeated several times in order to acquire a suitable population to verify data repeatability. Results showed the capability of the proposed approach of detecting a typical fault related to worn slippers. Future works will include tests in order to apply the approach to a wider set of faults and the development of a classifier for accurate fault identification.

A New Convolutional Neural Network-Based Data-Driven Fault Diagnosis Method

Fault diagnosis is vital in manufacturing system, since early detections on the emerging problem can save invaluable time and cost. With the development of smart manufacturing, the data-driven fault diagnosis becomes a hot topic. However, the traditional data-driven fault diagnosis methods rely on the features extracted by experts. The feature extraction process is an exhausted work and greatly impacts the final result. Deep learning (DL) provides an effective way to extract the features of raw data automatically. Convolutional neural network (CNN) is an effective DL method. In this study, a new CNN based on LeNet-5 is proposed for fault diagnosis. Through a conversion method converting signals into two-dimensional (2-D) images, the proposed method can extract the features of the converted 2-D images and eliminate the effect of handcrafted features. The proposed method which is tested on three famous datasets, including motor bearing dataset, self-priming centrifugal pump dataset, and axial piston hydraulic pump dataset, has achieved prediction accuracy of 99.79%, 99.481%, and 100%, respectively. The results have been compared with other DL and traditional methods, including adaptive deep CNN, sparse filter, deep belief network, and support vector machine. The comparisons show that the proposed CNN-based data-driven fault diagnosis method has achieved significant improvements.

Non-probabilistic reliability analysis and design optimization for valve-port plate pair of seawater hydraulic pump for underwater apparatus

Seawater hydraulic axial piston pumps are widely used in underwater apparatus systems in recent years. Reliability of the valve-port plate pair is vital to the performance of seawater hydraulic axial piston pumps. As the distribution information of the material combinations and working conditions of seawater hydraulic axial piston pumps are insufficient, the probability reliability analysis methods are not available for the valve-port plate pair. This paper develops a non-probabilistic reliability convex model for the valve-port plate pair. Firstly, the rotation of the pump cylinder is partitioned into six stages. Based on this partition, the dynamic models of contact pressure and pv value (the product of contact specific pressure and linear velocity) of the valve-port plate pair are derived by accounting for the pre-compression angle. Secondly, the marginal interval for the limiting [pv] value (It is the usual criterion to evaluate the critical operating conditions under which the material fails) of the material combination was obtained through adhesive wear tests. Thirdly, a limit-state function is then established based on the stress-strength interference model. Finally, the analysis and sea test results indicate that the reliability of the valve-port plate pair has significantly improved by adding auxiliary support on the port plate.

A Reliability-Based Robust Design Method for the Sealing of Slipper-Swash Plate Friction Pair in Hydraulic Piston Pump

In mechanical engineering field, sealing technology is of vital importance for the success of a product. A poor sealing design of a slipper-swash plate friction pair (SSPFP) could lower the reliability of a hydraulic piston pump and lead to the failure of the pump. In this paper, a reliability-based robust design method for the sealing of the SSPFP in hydraulic piston pumps is first established. The matrix expression of the relation between the numerical characteristics of the state function of the SSPFP and the random variables is derived. Methods for calculating the sealing reliability and analyzing the reliability sensitivity of the SSPFP in the hydraulic piston pump are provided. Then, the reliability-based robust design is formulated as a multiobjective design optimization problem to meet the reliability requirements. A numerical example is presented to demonstrate performance of the proposed sealing reliability-based robust design method.

Robust reliability-based optimization with a moment method for hydraulic pump sealing design

Reliability-based design (RBD) is widely applied to meet the reliability requirement at a reduced cost. Current RBD methods require complete distributions of basic random variables, but in real applications, such as the sealing design for hydraulic piston pumps, only statistical moments may be available. The reliability obtained from the RBD may also be sensitive to possible variations in distribution parameters or moments of basic random variables. To deal with these two challenges in the sealing design for hydraulic piston pumps, this study employs a robust reliability-based design methodology based on statistical moments. The optimization not only minimizes the sealing area of friction pairs, but also the sensitivity of the reliability. As a result, the reliability requirement is maintained with the increased robustness of the reliability. An improved higher moment (up to the forth moment) is also employed for higher accuracy with the associated analytical sensitivity indexes. The robust RBD methodology is successfully applied to the design of the seal of the slipper-swash plate friction pairs for a hydraulic piston pump. The application includes the reliability analysis, reliability sensitivity analysis, and robust RBD. The results demonstrate that robust RBD can produce more robust reliability than a traditional RBD methodology.

A transmissibility-based approach to identifying the dynamic behavior of a seawater hydraulic piston pump under pressure excitation

An investigation into the dynamic behavior of the piston pump is an important method to reduce its vibration and noise. In this paper, an approach to predict the dynamics of a seawater hydraulic piston pump (SWHPP) from output-only transmissibility measurements is introduced. In order to eliminate the harmonic interference generated by spindle rotation, the excitation in this method is the pressure which caused by the SWHPP operating at a constant speed and under different loading conditions. The first four modes of the SWHPP were estimated utilizing the method proposed in this paper, and the influence of the pressure on the dynamics of the SWHPP structure was further studied. The experimental results indicated that peak occurred around the frequency of 20 Hz, and the reason is that the estimated second-order natural frequency (19.8 Hz) is near to the frequency of 20 Hz which is the excitation frequency of the swash plate and the flat valve of the SWHPP. In addition, this method can identify modal parameters of the piston pump structure in the working state, so it can effectively predict the dynamic behaviors of the piston pump.

A Study for Development of Hydraulic Piston Pump for Driving Rescue Equipment

A Study for Development of Hydraulic Piston Pump for Driving Rescue Equipment