Dissertations / Theses on the topic 'Axial piston pump'

The piston/cylinder pair is the key lubricating interface of axial piston pumps. It suffers from excessive wear due to the huge lateral force, especially under high output pressure. In order to achieve predictive maintenance, it is significant to detect the performance degradation of the piston/cylinder pair. In this paper, a method to predict the wear of the piston/cylinder pair is proposed. The wear regions and corresponding wear depths under different conditions are investigated. The distributive characteristic parameters of the oil film are obtained, which can reflect the load-bearing and lubrication conditions at each region of the friction pair. Based on the oil film characteristic parameters, the most suitable wear model is chosen to calculate the wear depth, and then the entire wear profile of the piston/cylinder pair is obtained. The experimental investigation is carried out, and the results show that the accuracy of the wear regions and corresponding wear depth prediction is high. This method can be used to pump healthy management and choose the suitable working conditions of the axial piston pump.

En el ámbito de la Oleohidráulica, las bombas de pistón poseen los diseños más sofisticados, de hecho, las bombas de pistones son las únicos capaces de trabajar a altas presiones, además de poseer el mejor rendimiento de todo el grupo de bombas existentes. Sin embargo, cabe señalar que todos los diseños de las bombas de pistón, se basan principalmente en la experiencia de los diseñadores, por lo tanto no existen herramientas matemáticas para optimizar el diseño de las diferentes partes de las bombas. Por otra parte, en la actualidad hay empresas como Oilgear Towler, que inserta ranuras (surcos) en los patines deslizantes y en los pistones, (dos partes principales de estas bombas), pero no hay ningún estudio científico para analizar sus ventajas o desventajas. Por lo tanto, es necesario comprender matemáticamente las ventajas y desventajas debido a la presencia de ranuras en la superficie de diferentes partes de la bomba. Hay cuatro superficies de deslizamiento en las bombas de pistones, plato inclinado patín deslizante, barrilete y placa de cierre, pistón cilindro y junta esférica entre pistón y patín deslizante. Lubricación entre estas superficies es necesaria, apareciendo por tanto fugas de fluido a bombear entre las mismas. En este proyecto, nuestro objetivo es analizar cada una de estas diferentes superficies de deslizamiento por separado para comprender su diseño y el efecto de los parámetros de diseño en el comportamiento de la bomba. Una vez se tenga un buen entendimiento de las diferentes partes de la bomba de pistones, el objetivo es modelar el comportamiento dinámico de la presión y flujo en la salida de la bomba. En concreto se ha realizado: Conjunto plato inclinado, patín deslizante – Estudio de las características estáticas y dinámicas del patín deslizante, incluyendo la ranura tallada en el patín. Las ecuaciones de Navier Stokes en coordenadas cilíndricas se han aplicado entre el patín y el plato incluyendo la ranura. Los resultados presentados en este trabajo contemplan, distribución de la presión, las fugas de fluido, la fuerza y par sobre el patín, se ha estudiado la variación de dichos parámetros al modificar las dimensiones y posición de la ranura. El comportamiento dinámico del patín se ha tenido también en cuenta. Se estudia la posición de la ranura con el fin de optimizar el comportamiento del patín. Barrilete, placa de cierre.- Se analiza mediante la simulación de las ecuaciones de Reynolds de lubricación por FDM (método de diferencias finitas), la distribución de presiones, las fugas, la fuerza y los pares entre el barril y la placa de cierre. La fuerza total y los pares de torsión sobre el barril, se evalúan partiendo de la presión simulada, mostrando que los pares dinámicos que existen sobre el eje XX son mucho menores que los pares actuantes sobre el eje YY. . Pistón cilindro - Se ha investigado el comportamiento del pistón mediante la modificación del número de ranuras y su posición, la distribución de la presión en el intersticio pistón-cilindro, la fuerza sobre el pistón, las fugas y el par de torsión que actúa sobre el pistón se han analizado. También las zonas donde la cavitación es probable que aparezca se han presentado, se discute la forma de prevenir la aparición de cavitación a través del uso de ranuras. La ecuación de lubricación de Reynolds se ha modelizado en el intersticio pistón-cilindro mediante el uso de volúmenes finitos, la excentricidad y el movimiento relativo pistón-cilindro se han considerado. Diferentes configuraciones de ranuras han sido evaluadas con el fin de encontrar mínimas fugas, máximo par y mínima aparición de cavitación. Se especifican instrucciones de diseño para optimizar el comportamiento del pistón. Modelo dinámico de la bomba.- Se ha presentado un amplio conjunto de ecuaciones explícitas para cada parte con movimiento relativo de la bomba de pistones. Todas las ecuaciones se han validado mediante un análisis numérico y en su caso experimental. Las ecuaciones han sido combinadas para estudiar de forma dinámica las perturbaciones de presión y el caudal de fugas. El efecto de la pulsación de caudal cuando se modifica el diseño de la bomba también es presentado. En esta tesis, un modelo de simulación basado en ecuaciones analíticas se ha desarrollado, modelo que produce resultados muy rápidamente y aclara con mucha precisión el efecto de las fugas a través de los diferentes intersticios de la bomba.
In the field of Fluid Power, piston pumps possess the most sophisticated designs, in fact, pistons pumps are the only ones capable of working at high pressures, besides possessing the best performance (efficiency) of the entire group of existing pumps. However, it is noted that all the designs of piston pumps, are mostly based on the experience of the designers, thus there exist no mathematical tools for optimizing the design of the different parts of the pumps. On the other hand, there are now companies like Oilgear Towler, who inserted slots (grooves) in the slippers and in the pistons, (two major parts of these pumps) but there is no scientific study to analyze its advantages or disadvantages. There is therefore a need to understand mathematically to study the advantages and disadvantages due to the presence of the groove on the surface of different pump parts. There are four sliding surfaces in the piston pump, Slipper-swash plate gap, Barrel-valve plate gap, Piston-barrel chamber gap and Spherical bearing, where lubrication exists and leakages through these channels occur. In this project, our aim is to analyze each of these different sliding surfaces separately to understand its design constrains and the effect of the design parameters on the pump behavior. After having a better understanding of all the different parts of the piston pump, the aim is to model the dynamic behavior of pressure and flow at the outlet of the pump. Slipper plate gap - To understand static and dynamic characteristics of a piston pump slipper with a groove. Three dimensional Navier Stokes equations in cylindrical coordinates have been applied to the slipper/plate gap, including the groove. The results presented in this thesis include, pressure distribution, leakage, force and torque variations when groove dimensions and position are being modified, the effect of slipper tangential velocity and turning speed are also considered. Design instructions to optimize slipper/groove performance are also given. Barrel-valve plate gap - Present thesis, analyses the pressure distribution, leakage, force and torque between the barrel and the port plate of an axial piston pump by simulating Reynolds equations of lubrication by FDM (finite difference method). The overall mean force and torques over the barrel are evaluated from simulated pressure and it shows that the torque over the XX axis is much smaller than the torque over the YY axis. A detailed dynamic analysis is then studied by using the temporal torque calculated by Bergada. Piston-barrel chamber gap - It is being investigated the piston performance by modifying the number of grooves and their position, pressure distribution in the clearance piston-cylinder, leakage force and torque acting over the piston will be discussed, also the locations where cavitation is likely to appear will be presented, discussing how to prevent cavitation from appearing via using grooves. A finite volume based Reynolds equation model has been formulated for the piston-cylinder clearance which considers the piston eccentricity and the relative tangential movement between piston and barrel. Different configurations of the grooves have been evaluated in search of finding minimum leakage, minimum appearance of cavitation and maximum restoring torque. Design instructions to optimize the piston behavior are also given. Full pump Model - An extensive set of explicit equations for every pump gap will be presented. All of the equations will be checked via performing a numerical analysis of the specified pump clearance, the equations will then be combined to study dynamically pressure ripple and leakages. The effect on the flow ripple when modifying the pump design will also be presented. Therefore in present thesis, a simulation model based on analytical equations has been developed which produce very fast results and clarify very precisely the effect of different leakages happened through the pump clearances.

This thesis is concerned with the dominant leakage characteristics of an axial piston pump. Results have been obtained from a combination of analysis, Computational Fluid Dynamics (CFD) and experimental work, and have added to existing knowledge in this field. The measurement of slipper leakage within an axial piston pump is impossible due to additional leakage from the pistons and between the cylinder barrel and port plate. It may only be determined by analysis and this aspect has been studied via a new CFD simulation. Further progress has been made experimentally on slipper leakage. A new test apparatus was designed and developed by the author and comparisons have been made with parallel analytical work. Previous research in this area has concentrated on single-landed slippers and leakage rates from such slippers have been examined, however only under static conditions. The work in this thesis is the first to consolidate experimental studies on multiple-land slippers, and the first to measure slipper leakage under dynamic conditions. These results have been compared with both CFD simulations and a new theoretical study undertaken in parallel with this work. The new test apparatus allowed measurement of both leakage and groove pressure under a range of operating conditions. It was established that the presence of a groove reduces the restoring moment produced, and hence enables the slipper to operate with an appropriate angle of tilt, thus permitting hydrodynamic lift to more readily exist. However, this occurs at a cost of increased leakage. In addition to the experimental work on slippers, the time-varying pressures within selected cylinders of an axial piston pump were measured. In parallel, a fully dynamic CFD model of a pump was produced. This model included all leakage paths from the pump. It was discovered that the port plate leakage dominated the overall leakage, with slipper leakage still being significant, but with piston leakage insignificant. This model was also used to predict the flow and pressure ripple from the pump and the predictions were compared with experimental measurements.

This paper describes an investigation into the effects of fluid bulk modulus and traction coefficient properties on piston pump flow losses and radial pison motor torque losses through experimentation, modelling and simulation. Synthetic ester, high bulk modulus, multi-grade, and single grade mineral oils were evaluated. The high bulk modulus fluid exhibited 20% lower pump case and compensator flow losses than a conventional mineral oil of the same viscosity grade. Low traction coefficient fluids reduced the lowspeed torque losses of the radial piston motor by 50%. Physical models for pump case flow and motor torque losses were derived from the experimental data. Field data was collected from a hydraulically propelled agricultural machine. This data was used to model fluid performance in the machine. The simulation results predict that at an operating temperature of 80⁰C, optimizing the bulk modulus and traction coefficients of the fluid could reduce flow losses by 18% and torque losses by 5%. These findings demonstrate the potential of combining comprehensive fluid analysis with modeling and simulation to optimize fluids for the efficient transmission of power.

This master thesis presents a novel methodology for the  development of simulation models  for hydraulic pumps and motors. In this work, a generic simulation model capable of representing multiple axial piston machines is presented, implemented and validated. Validation of the developed generic simulation model is done by comparing the results from the simulation model with experimental measurements. The development of the generic model is done using AMESim. Today simulation models are an integral part of any development process concerning hydraulic machines. An improved methodology for developing these simulation models will affect both the development cost and time in a positive manner. Traditionally, specific simulation models dedicated to a certain pump or motor are created. This implies that a complete rethinking of the model structure has to be done when modeling a new pump or motor. Therefore when dealing with a large number of pumps and motors, this traditional way of model development could lead to large development time and cost. This thesis work presents a unique way of simulation model development where a single model could represent multiple pumps and motors resulting in lower development time and cost. An automated routine for simulation model creation is developed and implemented. This routine uses the generic simulation model as a template to automatically create simulation models requested by the user. For this purpose a user interface has been created through the use of Visual Basic scripting. This interface communicates with the generic simulation model allowing the user to either change it parametrically or completely transform it into another pump or motor. To determine the level of accuracy offered by the generic simulation model, simulation results are compared with experimental data. Moreover, an optimization routine to automatically fine tune the simulation model is also presented.

Thesis (Ph.D.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 28, 2007). Vita. Includes bibliographical references.

Axial piston pumps and motors are widely used in heavy-duty applications and play a fundamental role in hydrostatic and power split drives. The mechanical power losses in hydraulic piston pumps come from the friction between parts in relative motion. The improvement, albeit marginal, in overall efficiency of these components may significantly impact the global efficiency of the machine. The friction between slipper and swash plate is a functional key in an axial piston pump, especially when the pump (at low rotational speed or at partial displacement) works in the critical areas where the efficiency is low. The application of special surface treatments have been exploited in pioneering works in the past, trying different surface finishing or adding ceramic or heterogeneous metallic layers. The potential of structured coatings at nanoscale, with superhydrophobic and oleophobic characteristics, has never been exploited. Due to the difficulty to reproduce the real working conditions of axial piston pump slippers, it has been made a hydraulic test bench properly designed in order to compare the performance of nano-coated slippers with respect to standard ones. The nano-coated and standard slippers have been subjected to the following working conditions: a test at variable pressure and constant rotational speed, a test at constant pressure and variable rotational speed. The comparison between standard and nanocoated slippers, for both working conditions, shows clearly that more than 20% of friction reduction can be achieved using the proposed nano-coating methodology.

Markets show a clear trend towards an ever more extensive electronic networking in mobile and stationary applications. This requires a certain degree of electronic integration of hydraulic components such as axial piston pumps. Beside some wellknow approaches, the transmission of axial piston units still is relatively unexplored regarding electronification. Nonetheless there is a quite high potential to be optimized by electronic. In view of this fact, the present paper deals with the tribological contacts of pumps based on a demand driven hydrostatic relief. The contact areas at cylinder - distributor plate, cradle bearing and slipper - swash plate will be investigated in detail and it will be shown how the pump behavior can be improved considerably through a higher level of relief and a central remaining force ratio. The potential of optimization is to improve the efficiency, especially in partial loaded operation, power range, also for multi quadrant operation, precision and stability. A stable lubricating film for slow-speed running and for very high speeds at different pressures is ensured as well.

The displacement of the variable displacement pumps can be adjusted by changing the swivel angle of the swash plate. In fact, the swivel angle oscillates because of the oscillating torque on the swash plate, which caused by the pressure fluctuation of the piston chamber. The swivel angle is most often considered as a constant value in previous studies. However, the oscillation of the swash plate leads to an additional movement of the piston, which has an impact on the pressure fluctuation and the flow ripple. In this study, an improved model of a self-supplied variable displacement pump is established. The swash plate oscillation under different operating conditions is presented. In order to investigate the effect of the swash plate oscillation on the pressure ripple, a comparison between the case of the fixed swash plate and the oscillated swash plate is conducted. Results show the pressure ripple with an oscillated swash plate shows a smaller pressure ripple. It also shows that the nine pistons and the control mechanism both affect the pressure ripple and flow fluctuation.

Axial piston pumps are universal displacement machines that are used in a vast variety of applications. Their high pressure resistance and ease of operation make them very popular, especially in mobile applications. Some applications require more robust pumps with an extended lifetime, particularly those that operate in remote environments such as marine type or mining operations. Especially new applications like displacement control have high demands on pumps such as through shaft operation (many pumps on one shaft), high dynamics and multi-quadrant operation. These demands create challenges in terms of lifetime expectancy and robustness for pump manufacturers and machine OEMs. Currently most axial piston pumps go through a run-in process. During this process the softer bronze parts shave off and change their shape according to the necessary one for the pumps’ proper operation. This process is highly dependent on the design of the parts and their manufacturing tolerances. In this paper the run-in process of the slippers of an axial piston pump was investigated by means of measurements of the gap height and wear profile as well as simulation. The measurements show a clear change of profile and gap heights for the first 120 h of the pumps operation. After that the gaps stabilize. The numerical simulations made with the program Caspar FSTI were coupled with contact wear models to output wear profiles. Different models will be introduced and compared with measurements. Both the amount of material removed and the performance of the pump before and after run-in will be discussed.

The present study investigates the f ormation of tribolayers on bronze CuSn12Ni2. Two different test rigs are used, of which one is a sliding bearing test rig in order to perform lubricated thrust bearing tests. Bronze CuSn12Ni2 is used for the sliding elements and the counter body is made of C45 steel. In addition to that, an axial piston pump test rig was used to determine t he transfera bility of the results to th e axial pist on pump. The test conditions are set up in a way t hat the tribological load s in the contacts are similar to each other. Changes in the subsurfa ce morphology and the chemical composition of the tribolayer were analysed using electron pro be micro a nalysis (EPMA), trans mission electron microscopy (TEM), energy dispersive X -ray spectro scopy (EDS) and X-ra y photoelectron spectroscopy (XPS). Focused ion beam (FIB) milling was used to prepare site -specific TE M foils fro m the wear track. The formation of a nano scale tribolayer was associat ed with red uced wear, which leads to low leak age in the a xial piston pump. This tribolayer is enriched with oxygen, sulfur and zinc, which is an effect of tribochemical reactions of environment molecules and surface molecules.

In hydraulic pumps, typically in axial piston pumps, reduction of pressure and flow ripples was attempted by providing relief grooves and pre-compression for noise reduction. Pre-compression is normally achieved by using the dead space between pump ports in the valve plate. Also valve plate profile modification is required, if system operating conditions such as pump output pressure and flowrate change, to maintain optimum operating conditions for reduced pressure/flow ripple. An earlier simulation study confirmed effectiveness of varying dead centre position to reduce pressure and flow ripples. A specifically designed mechanism, outlined in the earlier work, achieves this goal by varying the dead centre position of the pump swash plate. This study reports on the findings of the effect of varying dead centre position and groove configurations on forces and moments acting on the swash plate for various operating conditions. The simulation model cited in the earlier work was used in this study. This information is vital for the design of an actuating mechanism to vary dead centre position of a pump valve plate. These simulations were run using MATLAB/Simulink and S-functions. Results of this study are promising.

This paper presents the development of a helicopter axial piston pump model with condition monitoring in mind. Industrial constraints and needs ask for modelling with a lumped-parameter approach and require model architecture to be addressed with care. The aim of the proposed model is to assess the merits of pump leakage monitoring through measurement of case pressure. Once reviewed the state of the art in pump modelling, the slipper/swashplate interface is taken as an example to propose and implement in Simcenter AMESim a variable gap height model. The simulation results show that commonly used lumped-parameter models overestimate leakage. It also points out that average leakage at slipper may reverse at high pump displacement.

This thesis is focused on study of piston pump with ball screw and submersed motor. Theoretic part is about study using pump and ball screw. Equations for description of pump, motor and ball screw are in computation part. And in last part is construction of pump and valve. Valve is computed in CFD.

The Master`s Thesis deals with design and construction of a valve block for a hydrostatic recuperative module of a vehicle with a direct application on pneu tyred roller AP 240H produced by the AMMANN company. The thesis aims to analyze recovery functions of the valve block in several operating modes of the roller, followed by a selection of the right hydraulic components from the perspective of predefined parameters and pressure differences. Design specifications are based on measurements and mathematical simulations on the experimental stand. The experimental stand for this application has been developed at 1:4 scale as compared to a real vehicle. The thesis includes also design of the supporting console for the module on the frame of the vehicle. The Master`s Thesis is a part of project EUREKA with cooperation Bosch Rexroth.

Different special brass (e.g. CuZn37Mn3Al2PbSi) and bronze alloys (e.g. CuPb15Sn) are well known for use in oil-hydraulics having in common to be alloyed with lead. The lead content of special brass alloys in this use ranges from 0.1 to 2.0 mass-%. Some bronze alloys provide even much higher contents of lead of 10 to 15 mass-%. Typically, lead is considered for improvement of machinability or castability. Beyond this purpose lead in brass and bronze alloys affects many more properties of manufacturing and application. During the shaping of the parts by means of hot or cold forming often the materials are strained close to their limits. Thanks to lead cracking is prevented during this process. Lead is also of great importance for the improvement of tribological systems. The surfaces of these systems are exposed to friction and wear. Lead is incorporated in the surface layers and supports the tribological system in their running-in process to achieve a steady state of friction and wear. Above all lead is unique because it forms no solid solution with copper or brass and forms no compounds with other typical copper alloying elements. The feasibility assessment of elements in order to substitute lead in brass or bronze alloys has to be done for each alloy and application individually. In oil-hydraulic applications as bushings, slippers or distributor plates, lead-free alloys must fulfil different profiles of requirements, depending on the conditions of manufacturing and application. The requirements do not only include mechanical strength, formability and thermal strength, but also fatigue strength, low friction and high wear resistance and lubricant compatibility. Consequently, the substitution of lead in brass and bronze alloys for application in oil-hydraulics is a challenging task. This does not only apply for the requirements for machining and forming, but particularly for the need of the new alloys to function under wear, friction and corrosion. Examples are given for how these challenges of new lead-free special brass alloys can be met in bushings (machining, friction properties), slippers (forming, strength) and distributor plates (fatigue strength) for axial piston pumps. Further on, new lead-free special brass alloys for contact with environmentally compatible lubricants are presented. All these examples show that there is not the one and only lead-free alloy for applications in oil-hydraulics. In fact, every application requires a different alloy which is composed and processed individually to meet the specific demands.

The use of water as a hydraulic fluid in a pump necessitates the use of conformal contacts to reduce the high rates of wear and leakage losses that result from the low viscosity and lubricity of water. Swashplate type axial piston pumps are ideal in this respect because they incorporate such conformal contacts. Furthermore, the development of such a pump for use with water, especially sea-water, critically relies on the correct selection and application of materials. The purpose of this research work is firstly to examine the contact conditions within an axial piston pump for a range of sleeved and lined components manufactured from a variety of different materials. The use of finite element analysis with gap elements is a useful way of determining the contact pressure distribution between conformally contacting components. It is shown that this method gives excellent agreement with available analytical methods for the two-dimensional cylindrical and axisymmetric spherical cases, and thus can be extended to layered components. Extension to three dimensions, when the contact cannot be accounted for by plane strain or plane stress conditions, is also possible, allowing a much more representative analysis of the contact conditions within an axial piston pump. No single combination of materials is identified as being the most suitable, rather, the method enables the consequences of choosing materials for their tribological characteristics to be examined. Once the contact conditions are known within the pump it is then possible to more accurately design the pump components. However, conventional deterministic methods are not appropriate for designing ceramic components, due to the inherent scatter of limiting defects, and statistical methods are necessary. Thus the second part of this research work is aimed at reviewing and examining the different probabilistic design methods with the long-term view of determining which, if any, are best suited to the design of ceramic components in this particular application. It is conduded that no single method adequately predicts the probability of failure of ceramic specimens with more complex stress distributions than four-point flexure bars.

Cette thèse présente une contribution à la surveillance des pompes à pistons axiaux des hélicoptères par modélisation et simulation. Un modèle de pompe à paramètres localisés est développé pour servir de banc d'essai pour les études de surveillance. L'auteur propose des améliorations de l'état de l'art de la modélisation à paramètres localisés des pompes à pistons axiaux, en se concentrant sur le besoin industriel de surveillance. La proposition se concentre sur la simulation du régulateur de pression dans des conditions dégradées, et sur le calcul des fuites de patin/plateau à travers un jeu de hauteur variable. Le modèle de pompe développé est comparé à des données expérimentales. Un outil graphique (la Courbe d'Identification des Dommages, DIC) est ensuite proposé. Cet outil permet d'isoler la dégradation de la pompe dans le système hydraulique à l'aide de mesures en régime permanent de la pression de refoulement et de la pression de drain. L'étude se termine par des recommandations pour augmenter le niveau de maturité technologique de l'approche proposée
This dissertation presents a contribution to helicopter axial piston pump monitoring through modelling and simulation. A lumped-parameter model of such pump is developed to serve as a virtual test bench for monitoring studies. As lumped-parameter models of axial piston pumps are less detailed than distributed-parameter models, the author proposes improvements of lumped-parameter modelling state-of-the-art, focusing on the monitoring industrial need. The proposal concentrates on the pressure compensator simulation in degraded conditions, and on the slipper/swashplate leakage computation through a variable gap height. The developed pump model is compared to experimental data. Then, a graphical tool is proposed, (the Damage Identification Curve, DIC), which allows for the isolation of pump degradation within the hydraulic system using discharge and case drain pressure steady-state measurements. The study is concluded by recommendations for increasing the maturity level of the proposed monitoring approach

Le travail présenté dans ce mémoire traite le diagnostic des pompes à pistons axiaux. Dans ce contexte, nous proposons différentes méthodes capables de diagnostiquer les fuites internes dans une pompe à pistons axiaux, notamment celles provoquées par l'usure d'un ou plusieurs pistons. Nous commençons ce manuscrit par un rappel des notions fondamentales liées à l'hydrostatique et nous expliquons le fonctionnement des pompes à pistons axiaux. Ensuite, nous abordons la modélisation et la simulation du comportement dynamique de ce type de pompe. Cette étape permet de comprendre les variations des grandeurs caractéristiques de la pompe (pression et débit). Après cela, nous comparons les signaux de pression simulés avec ceux acquis sur un banc d'essai expérimental. Ceci a pour but de démontrer la robustesse de la modélisation utilisée et de souligner les cas où la modélisation diverge de la réalité. Finalement, nous proposons trois méthodes de diagnostic basées sur différentes approches. Les deux premières visent à identifier le piston défectueux lorsqu'il y a fuite de piston. Ce sont des méthodes à base de modèle qui s'appuient sur l'estimation de grandeurs d'intérêts pour faire la décision du diagnostic. La dernière méthode, quant à elle, est orientée données. Elle exploite les données collectées pour différents états de santé (état sain et en présence de fuite de piston) et dans différentes conditions de fonctionnement (Vitesse et charge). Cette méthode se base sur plusieurs paramètres extraits à partir des données collectées. Elle permet de distinguer l'indicateur le plus robuste lorsqu'il s'agit de diagnostic de fuite de piston. Ceci, quelle que soit la condition de fonctionnement
The work presented in this thesis is intended for the fault diagnosis of axial piston pumps. In this context, we propose different methods able to diagnose internal leakages in an axial piston pump, in particular those caused by one or several worn pistons. We begin this manuscript by recalling the fundamental concepts related to hydrostatics and explaining the working principle of axial piston pumps. After that, we discuss the modeling and simulation of the behavior of this type of pump. This step is essential to understand the variation of characteristic variables of the pump (pressure and flow rate). Next, we compare the simulated pressure signals with those acquired on an experimental test bench. This is intended to demonstrate the robustness of the used modeling and to highlight cases where the modeling differs from reality. Finally, we propose three diagnostic methods based on different approaches. On the one hand, the first two methods aim to identify the faulty piston when there is a piston leak. These are model-based methods that use the estimation of interest parameters to make the diagnosis decision. On the other hand, the last method is data oriented. It uses the collected data for various health conditions and under different operating conditions (speed and load) in order to discriminate several classes. Each class corresponds to one health condition. This method offers the possibility to distinguish the most robust indicator that allows piston leak diagnosis, regardless of the operating condition

In hydraulic-mechanically controlled variable displacement pumps, the actual pump controller produces additional power losses. Due to the low damping coefficients of all pump controller’s components, hydraulic-mechanically pressure controlled pumps use to oscillate while adjusting the pressure level in the hydraulic system. In several state-of-the-art variable pump controllers, a damping orifice connects the control actuator’s displacement chamber with the reservoir. This bypass dampens the movement of the control actuator but also leads to bypass losses during steady-state operation of the pump. A new concept for damping via feedback loops avoiding bypass losses is presented in t his paper.

碩士
國立成功大學
機械工程學系
102
Axial piston pump with its high volume efficiency, high power density and long work life is widely used in engineering applications of hydraulic pump. It was important to develop its performance and to reduce the noise of axial piston pump during operation. Valve plate was a key component of axial piston pump. Its structure, material and precision which are either reasonable or not will affect the reliability, volume efficiency and work life directly. The pressure impact and flow fluctuation were the main sources of noise in hydraulic system during the piston pump operating. Design of valve plate structure was a main manner to reduce noises of axial piston pump, It is also important in this research. In this research, the flow field in axial piston pump was simulated using CFD to consider the flow characteristic during piston pump operating. In addition, the different working conditions of axial piston pump were also investigated. Based on results, we can know deeply the operation of axial piston pump mechanisms. Finally, the dimensions of buffer grooves of valve plate were designed to reduce the flow fluctuations and noises.

As part of the study involving the design and implementation of axial piston pump control systems, an accurate, dynamic model of a axial piston pump is required. In this thesis, the complete derivation of such a model is presented. The derivation is performed symbolically, using general geometrical coordinates and parameters of a typical axial piston pump, rather than specific values. Therefore, the developed model should be applicable to other types of axial piston pumps with similar configurations. The developed model is expressed by a set of highly nonlinear mathematical equations, these equations being functions of pump parameters and operating conditions. When the specific values of these various parameters were substituted into the describing equations, it was found, for the pump used in this study, that the model could be simplified to a set of linear expressions. In addition, the experimental results indicate that the developed model accurately predicts the dynamic response of a particular pump - a Vickers PVB5 axial piston pump.

The valve plate/cylinder block interface in an axial piston pump is often subject to extreme pressures, which can cause wear of the valve plate and ultimately, failure of the pump. The purposes of this study were to: a) experimentally investigate the film thickness generated between a floating valve plate and cylinder block in situ using proximity probes, b) develop a model which can predict the motion, film thickness and pressures of the floating valve plate and corroborate with experimental results, c) investigate surface pockets to provide additional lubricant at the valve plate interface by measuring the flow velocities and cavitation areas in a thrust washer bearing, d) numerically investigate surface modifications of the floating valve plate to observe any changes in lubricant pressure, temperature, cavitation, or valve plate deformation. Two different test rigs were designed, developed and used to investigate the performance of axial piston pumps and surface pockets. The axial piston pump test rig (APTR) was designed to operate and measure the steady state conditions of an axial piston pump. The APTR utilizes three non-contact proximity probes to measure the valve plate motion and film thickness between the cylinder block at various speeds and pressures. A thrust washer test rig (TWTR) was developed to measure the cavitation areas and flow velocities of lubricant in a pocketed thrust washer using μPIV. Through a novel interpolation approach, the depths of the micro-particles in the bearing pocket were determined using an analytical model. Using this approach, the μPIV measured 2D velocity field was employed to develop a 3D velocity field, which illustrates the fluid motion inside a pocketed thrust bearing at various speeds and viscosities. A dynamic lubrication model was developed using the thermal Reynolds equation augmented with the JFO boundary condition and the energy equation to determine the pressure, cavitation regions and temperature of the lubricant at the valve plate cylinder block interface. The lubricating pressures were then coupled with the equations of motion of the floating valve plate to develop a dynamic lubrication model. The stiffness and damping coefficients of the floating valve plate system used in the dynamic lubrication model were determined using a parametric study. The elastic deformation of the valve plate was also considered using the influence coefficient matrix approach. The experimental and analytical motion of the valve plate were then corroborated and found to be in good agreement. 4 and 8 pocket designs were then added as surface modifications to the floating valve plate in the dynamic lubrication model. The addition of surface modifications improved the lubricating conditions at the valve plate/cylinder block interface and resulted in increased minimum film thicknesses and lowered lubricant temperatures at the same operating conditions.

碩士
國立成功大學
工程科學系
104
This study consists of simulated high efficient axial piston pump operations. First of all, simulated the original pump. Secondly, search the literatures to design the original pump to reduce flow fluctuation rate, pressure fluctuation rate and acoustic power. Valve plate was a key component of axial piston pump. Its structure, material and precision which are either reasonable or not will affect the reliability, volume efficiency and work life directly. The pressure impact and flow fluctuation were the main sources of noise in hydraulic system during the piston pump operating. This research focuses on the flow fluctuation rate and pressure fluctuation rate of the axial piston pump. It was found that the proper design of the valve plate in an axial piston pump will dramatically lower the flow fluctuation rate and pressure fluctuation rate in the pump especially with regard to designs involving buffer grooves and a pre-compression reservoir. Optimizing the design parameters is intended to determine the best performance indices. As to the simulation results, the design of the valve plate in this research significantly improved the flow fluctuation rate and pressure fluctuation rate. In this research, Fluent CFD software was used to understand the flow characteristics of the piston pump’s outlet

Condition monitoring of hydraulic systems has become more available and inexpensive to implement. However, much of the research on this topic has been done on stationary hydraulic systems without the jump to mobile machines. This lack of research on condition monitoring of hydraulic systems on mobile equipment is addressed in this work. The objective of this work is to develop a novel process of implementing an affordable condition monitoring system for axial piston pumps on a mobile machine, a mini excavator in this work. The intent was to find a minimum number of sensors required to accurately predict a faulty pump. First, an expert understanding of the different components on an axial piston pump and how those components interact with one another was discussed. The valve plate was selected as a case study for condition monitoring because valve plates are a critical component that are known for a high percentage of failures in axial piston pumps. Several valve plates with various degrees of natural wear and artificially generated damage were obtained, and an optical profilometer was used to quantify the level of wear and damage. A stationary test-rig was developed to determine if the faulty pumps could be detected under a controlled environment, to test several different machine learning algorithms, and to perform a sensor reduction to find the minimum number of required sensors necessary to detect the faulty pumps. The results from this investigation showed that only the pump outlet pressure, drain pressure, speed, and displacement are sufficient to detect the faulty pump conditions, and the K-Nearest Neighbor (KNN) machine learning algorithms proved to be the least computationally expensive and most accurate algorithms that were investigated. Fault detectability accuracies of 100% were achievable. Next, instrumentation of a mini excavator was shown to begin the next phase of the research, which is to implement a similar process that was done on the stationary test-rig but on a mobile machine. Three duty cycle were developed for the excavator: controlled, digging, and different operator. The controlled duty cycle eliminated the need of an operator and the variability inherent in mobile machines. The digging cycle was a realistic cycle where an operator dug into a lose pile of soil. The different operator cycle is the same as the digging cycle but with another operator. The sensors found to be the most useful were the same as those determined on the stationary test-rig, and the best algorithm was the Fine KNN for both the controlled and digging cycles. The controlled cycle could see fault detectability accuracies of 100%, while the digging cycle only saw accuracies of 93.6%. Finally, a cross-compatibility between a model trained under one cycle and using data from another cycle as an input into the model. This study showed that a model trained under the controlled duty cycle does not give reliable and accurate fault detectability for data run in a digging cycle, below 60% accuracies. This work concluded by recommending a diagnostic function for mobile machines to perform a preprogrammed operation to reliably and accurately detect pump faults.

碩士
大葉大學
機械與自動化工程學系
106
In this thesis, parametric designs of a swash plate piston pump and a bent-axis piston motor are studied. Flow ripple rate and torque ripple rate while operating are known as the main causes for noises in swash plate piston pumps and bent-axis piston motors. In order to reduce noises and improve the flow stability, computational fluid dynamics (CFD) simulations for designs of a swash plate piston pump and a bent-axis piston motor are conducted. Firstly, the fluid with high rotational speed and pressure in grooves and pre-compression chambers are modeled by PumpLinx software. Using parametric design and CFD approachs, the designs of grooves and pre-compression chambers are optimized for output pressure, speed and volume. After that, the fluid pressure which is caused while operating are used to conduct stress analysis of the swash plate piston pump and the bent-axis piston motor. By investigating in on stresses and deformations of the structures, design’s rigidity is enhanced.

碩士
國立成功大學
機械工程學系
103
This study consists of simulated high efficient axial piston pump operations and is an attempt to decrease the flow fluctuation rate of the axial piston pump’s outlet. The operations of an axial piston pump can cause loud noises because interactions between solid structures and fluid in the pump create a pressure impact and flow fluctuations. This research is focused on the simulation of fluid dynamics in a pump and is an attempt to modify the pump design to reduce the flow fluctuation rate of the axial piston pump’s outlet. Special attention is paid to the influence of the valve plate on the flow fluctuation rate and on the coefficient of variation in the axial piston pump under consideration. It was found that the proper design of the valve plate in an axial piston pump will dramatically lower the flow fluctuation rate in the pump especially with regard to designs involving buffer grooves, damping holes and a pre-compression reservoir. Optimizing the design parameters is intended to determine the best performance indices. As to the simulation results, the design of the valve plate in this research significantly improved the flow fluctuation rate and coefficient of variation. In this research, Fluent CFD software was used to understand the flow characteristics of the piston pump’s outlet.

The scope of this study is to identify and modify the design parameters of the variable displacement axial piston pump in order to reduce its sensitivity to cavitation when operated in a hydraulic system with pre-established characteristics. An exhaustive analysis of existing theory explaining the cavitation phenomenon is performed and a new approach using the relationship between matter and energy is provided to complete and simplify the description of cavitation. A detailed mathematical model of the axial piston pump is created in order to evaluate the contribution of the pump's geometrical characteristics to cavitation. This model is validated using results from tests performed on two test units. Based on this, an evaluation method of the pump cavitation at the design stage is established and design recommendations are provided.

In this thesis a mathematical model is developed in order to describe the dynamics of the variable geometric volume swash plate axial piston pumps with the conical cylinder blocks and the integrated control unit. Using the validated model, an analytical study was conducted in order to investigate the effect of the port plate configuration on pump performance. Simulation of the change in the cylinder pressure and pump flow rate, in a systematic sequential procedure, led to an improved geometry for the suction and delivery silencing grooves on the valve plate. Cavitaion in the cylinder and pump noise were also reduced with the improved geometry. Force and vibration analysis of the pumping mechanism were carried out. This analysis presents some design recommendations regarding the moments acting on the swash plate, dynamic loads acting on the drive shaft bearings and the advantages and the limitations of using the conical arrangement of the pistons. Pump performance is simulated using a conventional PD controller with double negative feedback loop to control the swash plate swiveling angle, as currently used in practical applications. An introductory study of implementing other control schemes is conducted. A fuzzy controller is proposed to replace the PD controller in a double feedback control loop in order to improve the robustness of the control action. A single feedback control loop is proposed to replace the double control loop in order to suppress the steady state vibration of the swash plate. The control schemes were prototyped using specially developed real-time control techniques on a personal computer. The experimental setup is also used to verify the analytical findings of the pump performance with the newly proposed control schemes.

The advantages of high efficiency, reliability, flexibility and high power to weight ratio make axial piston pumps popular for use in a wide variety of applications like construction and agricultural machinery, off road vehicles and aerospace applications. However, a major drawback which limits their extensive use in other commercial applications is noise. One of the important components in axial piston machines is the valve plate, which influences the transition of the suction and delivery flows into and out of the displacement chamber. Appropriate design of the valve plate can play a significant role in influencing the rate of compression and expansion in the displacement chamber, and hence contribute towards the abatement of noise in axial piston machines. Furthermore, the relief grooves in valve plates makes them relatively less sensitive to operating conditions for the operation of the pump. The high sensitivity of the valve plate design towards the pressure build up in the displacement chamber and towards the noise sources are big motivation factors towards rigorously exploring the design space to find suitable designs to meet the objective of noise reduction. This motivates the development of an advanced computational tool, colloquially called 'MiNoS', where a powerful optimization algorithm has been combined together with a novel parametrization scheme for valve plate design and a 1D simulation model of swash plate type axial piston machines to find optimized designs which can contribute towards noise reduction in swash plate type axial piston machines. Furthermore, incorporation of the appropriate constraint also helps in avoiding designs susceptible to the onset of cavitation in the displacement chamber. A case study performed using the developed computational tool has been shown later in this work.

Rolling mill automation systems started nearly in 1960s when the servo system was introduced to the metal forming industry. During the past decades, hydraulic control systems have found increased applications in rolling mills in an attempt to cope with the harsh environment conditions and the high power demands for metal forming. During the rolling process, both rolling speed and rolling load must be controlled in accordance with the independently varying torque that disturbs the control system. This project is concerned with the development of an electro-hydraulic control system in order to control both rolling speed and rolling load with minimum number of components. A mathematical model of a pressure compensator is constructed and a simulation program based on Matlab-Simulink is developed to simulate both the static and the dynamic characteristics of the entire control system. The control system has very good flexibilities to various rolling mill requirements, and it is very convenient to adjust due to different variable load demands. An experimental setup composed of real time control software and a hydraulic test bed is built in order to validate the compensator mathematical model and verify the control system simulation results. The simulation and experimental results are compared and discussed.