Abstract: The thermal behaviour of aircraft hydraulic systems is a critical issue in systems design especially when no heat exchangers are incorporated. Thermal stability has to be guaranteed for a large variety of ambient conditions and operational modes. Introducing HEPCUs (hydraulic-electrical power con-version units) into the system architecture even deteriorates the thermal balance due to higher power losses and extended operation periods. This paper describes the development of a thermal model for an conventional aircraft hydraulic system using Matlab/SIMULINK. This model is validated with measured data for typical mission profiles. A thermal HEPCU model is added in order to simulate and evaluate the influence of the HEPCU integration on the basic architecture.

Keywords: HEPCU, hydraulic-electrical power conversion unit, aircraft hydraulic system, thermal simu-lation

Contact: Joerg ENGELHARDT, Technical University of Hamburg-Harburg, Institute for Aircraft System Engineering,  Nesspriel 5,  D-21129 Hamburg, Germany
 

Abstract: The roller press is widely used in grinding material due to its high efficiency and power saving. It becomes the fast-developing grinding-equipment. In grinding process, the stochastic variance of granularity,flux,density of materials leads the forces on the moveable roller and hydraulic system are stochastically varied. The clearance between rollers is also varied. While the fluctuation of the clearance is too large, it induces that the bad adaptive to materials and low grinding efficiency. Therefore, it is significant that keeping the clearance stabilization by controlling the vibration of moveable roller and hydraulic system. In this paper, a model of the vibration control is established, based on the principle of the roller press. The control strategy is put forward by variable structure control. A simulation is given.

Keywords: moveable roller, roller press, variable structure control, hydraulic system

Contact: FU Hua, FU Choudong, WU Genmao, State Key of Fluid Power Transmission & Control, Zhejiang University, Hangzhou,  370027, P. R. China
 

Abstract: In this paper we would like to present the current state of analysis and work on the activities carry out in the first year of our studies. The aim of these activities was to study the suction performance of the Gerotor pumps and it is influence on the fluid-borne noise generated. This work is presented in three levels: geometry, simulation and experimentation. The geometric study allows us to penetrate the knowledge of the trochoidal profiles and assists in the optimisation of them. The different methods of calculation and the simulations allow us to evaluate the fluid-dynamic performances and the influence of the input and output impedance. We would like to emphasize the exhaustive use of Bond Graph simulations. In the last level, the models have to contrast experimentally with the test benches that are described in this paper.

Keywords: trochoidal-type pumps, contact stress, photoelasticity, Bond Graph and fluid-dynamic

Contact: Pedro Javier GAMEZ-MONTERO, Esteve CODINA MACI?, Technical University of Catalonia, Department of Fluid Mechanics, Campus Terrassa. C/ Colon n 7-11. 08228. Terrassa. Barcelona. Spain
 

Abstract: This paper deals with the first investigations of rotary seals. Opposed to rod seals, rotary seals are axially fixed on the shaft and therefore working under insufficient lubrication conditions. Because of this the physical processes in the sealing gap of rotary seals have been almost unknown until now. Different seal designs are tested experimentally and are simulated by FEA in regard to friction torque, stress-strain behaviour and thermal aspects. A close correlation between simulations and measurements can be found (e.g. linear dependence of torque on pressure). Different designs of seals (one-part and multipart) are compared. Furthermore, it is shown, that an undulation of the seal edge compensates for the disadvantage of insufficient lubrication of the sealing gap, in that a speed component in axial direction is forced by the bevelled seal edge during rotational movement of the shaft. By that oil is conveyed under the seal and thus the frictional behaviour is improved.

Keywords: rotary seals, biodegradable fluids, FEA, measurement of friction torque, undulation

Contact: Dipl.-Ing. Martin GOERRES, Institute of Fluidpower Transmission and Control (IFAS),  RWTH Aachen, Steinbachstr. 53, 52074 Aachen Germany, Phone: +49 (0) 2 41  80 75 24
 

Abstract: The present paper addresses the regulation of weakly damped aeroelastic wing structures by means of the primary flight controls (PFC). Synthesizing a  sufficient loworder linear multi model system of the aggregate aeroservoe-lastic plant requires the design of a robust state feedback. This ensures a remarkably augmented damping ratio in comparison with the original aeroelastic system. Moreover, the influence of the actuation system performance on the aeroservoelastic damping augmentation feedback is investigated. The suitability of the resulting controller is verified by simulation as well as validated by real tests.

Keywords: aeroservoelasticity, flexible aircraft, analytical modelling, structural vibrations, typical section, primary flight control actuation system, hydraulic actuator, uncertain paramters, robust control, parameter space design

Contact: Udo B. CARL and Marcus H. GOJNY, Technical University of HamburgHarburg, Institute of Aircraft Systems Engineering (2.08), 21071 Hamburg, Germany
 

Abstract: This paper presents a new joint integrated rotary servo actuator design for heavy load mobile manipulators and robots. The current state of actuator technology in mobile machines is discussed briefly. A new solution for a pump controlled joint integrated actuator is proposed. For end effector axes this design is ideal for electrical power distribution, known as power by wire. Two different control strategies are presented and discussed in its advantages and disadvantages.

Keywords: mobile robot, pump control, joint integrated servo actuator, control strategy, automatic control

Contact: Jörg GRABBEL, Technical University of Hamburg-Harburg, Institute for Aircraft Systems Engineering, Nesspriel 5, D-21129 Hamburg, Germany
 

Abstract: This paper is the current status summary of a Ph.D. work, which subject is the hydraulic external gear pumps, with pressure compensated lateral plates. Concretely, the aim is to determinate the behaviour of the plain journal bearing, i.e. found theoretically and experimentally, the orbits of the shaft v.s. the lateral floating plate, where the bearing is located. The Thesis is a part of an European project, concretely a Brite-Euram project centred on investigating the performance of an existing gear pump, focused to the industry site and, in this case, to the Spanish manufacturer of the pump being studied, the company Roquet, S.L. For this reason the aim of the finite element simulation is to give support to the experimental results, being these the most important part of this Thesis. Subsequently a summary of the theoretical work done, that is finding the orbits of the shaft by FEM integration of the 2D Reynolds equation will be explained. 
As well, measurements of the shafts orbits, and movements of the lateral plates on a real unit under pressure are shown. These measurements are done without contact by laser probes.

Keywords: gear pump, plain journal bearing, Reynolds Equation, orbit, floating lateral plate.

Contact: Marius GUTÉS, P.J. GÁMEZ MONTERO, Roberto CASTILLA, Dr. Esteve CODINA, Technical University of Catalonia, Fluid Mechanics Department, Terrassa Campus. C/ Colon n?7-11 (08228) Terrassa. Barcelona. Spain
 

Abstract: There are only few water hydraulic high pressure pumps in the market and most of them are very expensive to buy and maintain. A Finnish company has developed a new type of water hydraulic intensifier pump in which the control valve is integrated in the plunger. This means faster response in the change situation of the plunger and more compact size of the pump. The prize of the pump is also reasonable. This paper deals with the optimization of the intensifier pump using computer simulation and experimental measurements. The aim of the work is to improve the characteristics and reliability of the pressure intensifier pump. The effect of integrated control valve characteristics to intensifier pump properties is discussed. The optimum performance is studied via variation of significant parameters of the intensifier pump. The other aim of the work is to develop a reliable water jet cutting system for paper machine industry. The intensifier pump is to be used in the water flow source in the cutting system. One other aim of the work is to increase the basic knowledge of water hydraulics and to increase the life time of the water hydraulic components used in water hydraulic systems which has high demands for reliability.

Keywords: water hydraulic, jet cutting

Contact: HYVÖNEN M., KOSKINEN K.T., and VILENIUS M.J. , Tampere University of Technology, Institute of Hydraulics and Automation, P.O. Box 589, 33101 Tampere, Finland
 

Abstract: The paper contains the survey of the problems of the timber cutting process. It concentrates on the forest machines, which are working in cut-to-length method. The cutting function is an essential part of a harvester work. Cutting systems must operate efficiently and reliably in harsh field conditions. Additionally timber cutting is a fast process, which happens in a couple of seconds. The quality of cutting is the most significant feature of the saw. Trees should be cut without causing damage on the surface of the tree. However the bucking splits of stems are a main problem of the cutting process. It has been studied that even 70 % of stems have cutting damages. The bucking splits reduce the amount of useful material. The faster a log is bucked, the lower the risk of splits occurs. Although the operator and cutting tools has a remarkable influence on cutting quality, the main development work is to decrease cutting time with closed loop electrohydraulic control. The paper deals with problems that are faced with the cutting process. In addition the reasons and the results of these problems are considered. Also the potential solutions to avoid problems in timber cutting are discussed commonly.

Keywords: hydraulics, forest machines, timber cutting

Contant: Juha INBERG,  Institute of Hydraulics and Automation, Tampere University of Technology,  P.O.Box 589, FIN-33101 Tampere, FINLAND
 

Abstract: Mobile hydraulics include fluid power components and systems utilized in mobile machinery such as forest machines, excavators and hydraulic lifts. It has special features compared to the stationary i.e. industrial hydraulics. This paper gives an overview of mobile hydraulics and presents the benefits that can be achieved by employing modelling and simulation in order to carry out R&D of such machines.
Keywords: mobile hydraulics, modelling, simulation, R&D

Contact: Timo. J. KÄPPI, Tampere University of Technology, Institute of Hydraulics and Automation, P.O. Box 589,  FIN-33101 Tampere, FINLAND
 

Abstract: Cavitation consists of evaporation and condensation of a liquid. Cavitation normally occurs when liquid at constant temperature is subjected to vapour pressure. In fluid power applications the evaporation pressure is reached when flow velocity is increased sufficiently. The occurrence of cavitation in fluid power is mostly detrimental.  One of the devastating consequences of cavitation is the mechanical degradation of a solid material (cavitation erosion). Because cavitation is mostly harmful to the system it is to be avoided as far as possible. When actions for preventing cavitation are considered, it is essential to recognise the existence of cavitation and location of cavitation inception point. Direct detection of cavitation is often impossible due to the complicated constructions of fluid power components. Due to restrictions of direct detection of cavities, various indirect methods can be used. In this paper, cavitation phenomenon is explained and effects of cavitation on the system are dealt with. Cavitation erosion mechanisms are described and parameters affecting the degree of formed cavitation erosion are discussed. Various methods for cavitation detection are presented.

Keywords: Fluid power, Cavitation, Cavitation erosion, Detection of cavitation

Contact: Timo KOIVULA Tampere University of Technology, Institute of Hydraulics and Automation, P.O.Box 589, 33101 Tampere, FINLAND
 

Abstract: Seal friction of pneumatic cylinders possesses uncertain properties due to the interference of various factors, and it causes random oscillation or stick-slip when the piston is driven at extremely low speed. A deeper under-standing of the friction force is required for avoiding this oscillation phenomenon, which results in a deterioration of performance. This paper focuses on analyzing the oscillation phenomenon appearing in time responses of the driving velocity of the piston. In order to investigate aspects of velocity responses in a meter-in and meter-out circuit, we first use an analytical approach with a mathematical model including the friction force under some assumptions. An experimental study is then performed, showing the relationship between an effective sectional area of control valves and oscillatory behavior. It also shows by using some chaos indices, such as Lyapunov exponents, that the behavior of piston velocity turns chaotic under certain conditions in actual situations. In addition, the effects of changes in both supply pressure and load are examined. Based on both theoretical and experimental results, we confirm that the oscillation is caused by the nonlinear friction force.

Keywords: Pneumatic Cylinder, Friction Force, Stick-Slip, Chaotic Oscillation

Contact: Takahiro KOSAKI and Manabu SANO, Hiroshima City University, Department of Computer Science, 3-4-1, Ozuka-higashi, Asaminami-ku, Hiroshima, 731-3194 , Japan
 

Abstract: In this study, we deal with a bilateral master-slave system for tele-robotics composed of electro-hydraulic servo-systems. In a teleoperated master-slave system, the master has to play two roles, firstly as a reference input device to the slave and secondly as a haptic display device. The term haptic display indicates a function by
which the operator can feel a force fed back from the slave. In order to produce a haptic display composed of hydraulic servo-systems, we must solve a problem called back-drivability, in which an actuator in a hydraulic servo-system cannot be operated freely by manual means. As a practical solution to this problem, we propose a
driving method of actuator that uses a force sensor attached to the actuator. Furthermore, as an application of the haptic display proposed, we construct a bilateral master-slave system composed of electro-hydraulic servo-systems. Experimental results of the manipulating motion of the system are given.

Keywords: Hydraulic Servo-system, Master-slave System, Haptic Display, Tele-robotics

Contact: Shigeki KUDOMI, Gifu Prefectural Research Institute of MIT (Ph.D Student in Gifu Univ.), 4-179-1 Sue-cho, Kakamigahara, Gifu, JAPAN
Contact: Dr. Hironao YAMADA, Associate Professor, Gifu University, 1-1 Yanagido, Gifu, JAPAN
Contact:  Dr. Takayoshi MUTO, Professor, Gifu University, 1-1 Yanagido, Gifu, JAPAN
 

Abstract: The lubricating gap represents one of the central design elements in displacement machines. An optimal gap geometry, i.e. gap shape and surface quality, influences significantly the efficiency, life, reliability and costs of the machine and thus of whole fluid power systems. The influence of the surface asperity has been investigated by means of friction measurements at the piston/cylinder assembly at the rotating group of an axial piston machine, varying the piston surface qualities. The rapid improvement in the field of production technology within the last years offers new opportunities for an optimization with regard to the gap design. In particular,
the application of a high precision hard turning process to the production of pistons for axial piston machines allows a piston shape, differing from the conventional cylindrical form. The piston shape itself has a strong impact on the flow and the load capacity of the gap and thus influences the energy dissipation. The designers
may now ask themselves, which shape is the most reasonable one. This paper intends to contribute to an answer by means of simulation and measurement.

Keywords: axial piston machine, piston/cylinder, tribology, friction force, gap geometry, surface quality

Contact: Dipl.-Ing. Rolf LASAAR,  Technical University of Hamburg-Harburg,  Institute for Aircraft Systems Engineering, Nesspriel 5, 21129 Hamburg, Germany
 

Abstract: The subject of the presented research project is the exact knowledge about the parameters influencing the operating characteristics and limiting the maximum power of low pressure hydraulic vane type machines, used as drives for ship-deck machinery, to obtain a full utilisation of the potential of these motor type, and the interaction between biodegradable hydraulic fluids and hydrostatic units of the motors. To improve the operating characteristics of this motor type, several measures, like the application of friction- and wear-reducing coatings as well as the fitting of synthetic or ceramic insets at the highly stressed contact areas shall be evaluated.
The state of the art, concerning the influence of geometrical and physical parameters and the fluids properties on the total efficiency of hydrostatic motors is constrained on fast-moving devices or equations of general validity. For that reason a mathematical model of a low-pressure, slow-moving, high torque vane type motor was developed for the determination of volumetric and hydraulic-mechanical power dissipations. Knowledge about the behaviour of biodegradable hydraulic fluids, their influence on component wear and energetic efficiency of the motor and the change of fluid-characteristics and -performance under the special conditions of a ship-deck machine was obtained by bench-tests.

Keywords: Ship-deck Machinery, Low pressure Hydraulics, Mixed film Lubrication, Bench-tests,
mathematical Model, Power Dissipation, Biodegradable Hydraulic Fluids,

Contact: Dipl.-Ing. B. KUTTER, Prof. Dr.-Ing. D. G. FELDMANN, Technische Universität Hamburg-Harburg, Arbeitsbereich Konstruktionstechnik I, Denickestr. 17, D-21073 Hamburg, Germany,  Phone +49 40 42878-3231, Fax +49 40 42878-2296
 

Abstract: There is an effective trend using input energy of dynamic systems nowadays. It is the same in the branch design and control of electrohydraulic systems. We try to develop systems characterised by high efficiency coefficients.  Standard electrohydraulic systems are characterised by low efficiency. A pump produces oil characterised by constant pressure and constant flow. As a result of this is energy wasted by stranglehold and by the pressure issue of the system. There are systems characterised by a higher coefficient of efficiency. The systems with constant pressure, which has better results and the Load-Sensing systems. The Load-Sensing system is the best, because the wastes by stranglehold and by the pressure issue system are minimal. There are more ways, how to realise such a load-sensing system, but the start point is the same. The flow is given by multiplication of speed and volume. So, if we want to change flow, we can do it by changing volume or speed of the pump. The first way is hydraulic load-sensing system and second one is electrohydraulic Load-Sensing (there is also third method  to change both of them). I am interested in the electrohydraulic load sensing system. In my way it consist of an asynchronous motor controlled by a frequency changer and a pump with constant volume. I assume, this concept is very useful, because it consists of parts with uncomplicated structure, which means no problems during work. The main part of my paper goes in the electrohydraulic Load-Sensing system. The scheme of this system is presented and itemised. There are presented models of items and solution of control circuits in the paper as well as the result of the simulation.

Keywords: Load-Sensing system, Frequency changer, Asynchronous motor, Hydraulic system

Contact: Radek MANASEK, Department of Control Systems and Instrumentation  352, V B-TU Ostrava, 17. listopadu 15, 708 33, Ostrava  Poruba, Czech Republic
 

Abstract: This paper describes the system analysis and control design of an electrohydraulic servo-drive using a nonlinear composite feedback control approach based on singular perturbation theory (Kokotovic, Khalil & OReilly 1986). A comparison with linear output feedback (P-control) and linear state feedback (LQR-design) shows the bene? ts of the proposed method. The nonlinear control design features feedback linearization of the slow system (reduced system, corresponding to the incompressible model) and simple proportional feedback of the pressure difference (fast system). Experimental results are given for step responses and sine tracking.

Keywords: hydraulic drives, nonlinear control, composite feedback, singular perturbation

Contact: Bernhard Manhartsgruber, Department of Mechanics & Machine Design, Johannes Kepler University, Altenbergerstr. 69, 4040 Linz, Austria
 

Abstract: Numerous hydraulic sources create significant flow- and pressure pulsations. Common measures to reduce these unpleasant effects include accumulators, in particular featuring a 'Pulse-Tone' design, shock absorbers in various arrangements and novel multiple-volume resonators. In this paper I will compare conventional devices to 3 novel concepts of solid-body compensators, i.e. compensators based on a multi-degree of freedom mass-spring system, compact l/4 side branch resonators and compensators based on various arrangements of plate/shell elements. For this comparison, I will use criteria, such as the adjustment of the resonance frequency, mechanical stresses in the resonator, the ability to compensate frequencies which are integer multiples of a base frequency as well as compact and cheap design.

Keywords: Hydraulics, Pump, Noise, Attenuation

Contact: Josef MIKOTA, Johannes Kepler University of Linz, Institute for Mechanics and Machine Design, Altenberger Str. 69, A-4040 Linz, Austria
 

Abstract: An Electro-Hydraulic Servovalve is an essential item of servomechanism where fast speed of response, high power output and working fidelity are necessary. Two major components of the present single-stage valve are a spool valve and a linear force-motor. The present work includes lumped and chiefly one-dimensional, non-linear field modelling of hydraulic fluid in the spool valve and magnetic flux in the motor. Computer aided design and sensitivity analyses of static performance have been carried out. In the sensitivity analysis, effects of radial clearance, port lap conditions, mismatch in the areas of the tractive air-gaps and port geometry on valve per-formance have been studied.

Keywords: EHSV, modelling, design, lap, flow-gain

Contact: Saikat MOOKHERJEE, Jadavpur University, Project NEPTUNE, Department of Mechanical Engineering, Calcutta-700 032, INDIA
 

Abstract: The servodrive analyzed here consists on a large stroke actuator of 2 meters, activated by a flow proportional valve. The aim of the Ph.D. is to achieve a successful control of the actuator despite it having big chambers, which has a big influence on the system response, owing to the air compressibility. For the experimental study, a test bench has been built and a magnetorrestrictive sensor of displacement is used in order to close the loop. Before starting the control of the system and in order to know how the pneumatic servo drive reacts, the interaction of the actuator and valve set has been studied by means of Bond Graph technique.
At first, the PID control was applied in pneumatic servodrives, after seeing its several problems, state control algorithm started to be applied. The state loop control algorithm reaches a good result, however in cases where a system parameter changes it is necessary to retune the state variable gains (position, velocity and acceleration), above all in this particular case. It is here where Fuzzy Logic reasoning could be used.

Keywords: Servo pneumatic drive, bond graph, state loop control, fuzzy controller.

Contact: Hipolit MORENO LLAGOSTERA. Eng.., Salvador de las Heras Jimenez Dr. Eng. (Thesis Director), Dpt. Mecánica de Fluids - UPC. Campus de TERRASSA.C/ colón 7-11, 08225 TERRASSA. Barcelona, SPAIN
 

Abstract: The filtration efficiency of hydraulic filters is generally defined using the standardised Multi-pass test. The test conditions of the Multi-pass test are very stable, which is often inconsistent with the real-life working conditions. This may cause a substantial decrease of the expected filter performance in real use. This paper presents a test unit and test procedure that were developed and used for the testing of hydraulic filters with variable flow. The aim of the research is to test the filtration efficiency under conditions, which are corresponding to real-life working conditions. The developed test unit was in principle as a normal Multi-pass unit but in addition it enabled the use of flow variations and the controlling of particle concentration in the upstream of filter. The test procedure included a flow pattern in which both constant and peak flow phases were combined. The main parameter of the pattern, which was used in tests, was the flow amplitude. A series of filter elements were tested
using four different flow amplitudes. The presented efficiency curves serve the selection of filter and the evaluation of filtration efficiency under variable flow conditions. The test unit will be utilised in the development of a new filter solution for variable flow.

Keywords: Fluid power, Filters, Tests, Variable flow

Contact: Petteri MULTANEN, Tampere University of Technology, Institute of Hydraulics and Automation, P.O. Box 589, 33101 Tampere, Finland
 

Abstract: The goal of the thesis described in this paper is to improve the control of mobile hydraulic cranes. The thesis is split into five parts: a requirements analysis, an analysis of the current systems and their problems, an analysis of different possibilities for system topologies, development of a new control system for the near future based on electro-hydraulic separate meter in / separate meter out valves, and finally an analysis of more advanced and complex solutions which can be applied in the more distant future. The work of the thesis will be done in cooperation with industry so the thesis will have more of an industrial focus than a purely theoretical focus.

Keywords: Mobile Hydraulic Cranes, Control Strategies, Separate Meter-in/Separate Meter-out.

Contact: Marc E. MÜNZER, Aalborg University, Institute of Energy Technology,, Pontoppidanstr?de 101, DK-9220 Aalborg, Denmark
Email: mmun@iet.auc.dk