In this thesis a fault detection technique for a high performance hydrostatic actuation system was developed and evaluated. The
extended Kalman filter (EKF) was used for parameter identification and was applied to an electrohydraulic actuator (EHA) and the
performance of the technique was discussed. The EHA is a high performance, closed loop actuation system consisting of an AC
variable speed electric motor, bi-directional gear pump, an accumulator, check valves, a cross-over relief valve, connecting tubes and
a custom made symmetrical actuator. The EHA has potential applications in the aerospace industry as flight surface actuation and in
robotics. Failures in the EHA can pose a safety hazard and unscheduled maintenance can result in costly downtime. Fault detection in
the EHA will increase its safety and efficiency.
The proposed predictive maintenance strategy involves monitoring the EHA by estimating two parameters, namely the effective
bulk modulus and the viscous damping coefficient. Lowering of the effective bulk modulus, as a result of air entrapment, will affect
the response of the EHA and may cause stability issues, by lowering the bandwidth of the system. Changes in the damping coefficient
for the actuator can indicate deterioration of the oil, wear in the seals or changes in external friction characteristics. The parameters
were estimated using EKF and changes in the estimated values were related to faults in the system. Simulation studies were used
to investigate the feasibility of the approach and experimental results were obtained. The study investigated system observability in
order to improve the performance of the filter in estimating parameters. The estimations were successful and the EKF was also able
to detect and estimate faults which were introduced in the EHA. In this study, the friction characteristics of the symmetrical actuator
in the EHA was also investigated and a novel friction model was proposed. The EKF identified the friction characteristics using
simulated and experimental data. In summary, the application of the EKF technique to the EHA has produced very promising results.
Practical and powerful millimeter-sized micromachines such as micro maintenance robots for small diameter pipes of power
plants and microfactories have been required and micromachines using fluid power have been investigated. The paper proposed and
developed novel microvalve, micropump and micro fluid power system using those components.
First, a novel microvalve using MR (magneto-rheological) fluid valve-body was proposed and developed. The valve has an MR
fluid column in flow channel as a valve-body that is supported by permanent magnets and is deformed by an electromagnet to control
the opening. A microvalve was fabricated with
Second, improvements of a piezoelectric micropump using inertia of pipe that is attached in place of an outlet check valve were
investigated. A nonlinear mathematical model with lumped parameters using a virtual tank was established and the pipe size to increase
the output power was obtained through simulations and experiments of fabricated micropumps with 2.3cm3 in volume.
Finally, a position control microsystem was fabricated using the developed microvalve, the micropump, and a bellows microactuator.
The characteristics were experimentally clarified and the validity was confirmed.
For global-warming prevention and earth-environment protection, reduction of energy consumption becomes important problem
in all industrial fields. In the field of oil hydraulics, the secondary control system is one of the energy-saving systems, because it
makes possible to recover and reuse the kinetic energy and the potential energy of load by using variable displacement pump/motor
(VDPM) connected to a constant pressure supply. In Germany, this system has been studied from the 1980ís and applied to many
types of equipments. In Japan, Constant Pressure System (CPS) was proposed and hybrid hydraulic vehicle is being studied.
For lifting equipment and press machines with hydraulic cylinders, a hydraulic transformer is used for recovering potential energy
of load. The transformer is a combination of the VDPM and a fixed displacement pump/motor (FDPM) connected on the same
shaft. It is reported that the power of 1000ton press machine is lowered from 1300kW to 400kW by hydraulic transformer.
In this paper, the position control and the energy-saving effect of a hydraulic cylinder drive system using FFC (Fluid Force Couple)
type transformer, which consists of two FFC pump/motor, are investigated. The outline is as follows.
First, the characteristics of CPS are analyzed. In drive systems using VDPM, the displacement of VDPM is proportional to the
output torque and the transfer function from displacement to output position is a second order system. In drive systems using hydraulic
transformer, the displacement of VDPM is proportional to the output pressure and the transfer function from displacement of
VDPM to the position of cylinder is also a second order system. The displacement of VDPM is adjusted in closed loop control. In the
case of cylinder velocity control or position control, the response of the displacement of VDPM is much higher than that of the transformer
and the cylinder, so this inner loop is regarded as a unity element in outer loop design.
Next, the experimental equipment with a double acting cylinder and a load in vertical direction is built up. The displacement control
of the VDPM and the pressure control of a constant pressure source are designed.
Next, the position control of cylinder using the hydraulic transformer is discussed. Nonlinear friction torque, leakage flow of the
transformer, and load force of cylinder are disturbance in the position control system. So the multiple closed loop control and twodegree-
of-freedom control are used. The multiple closed loop control system consists of displacement feedback loop of VDPM,
velocity feedback loop of cylinder and position feedback loop of cylinder. The advantage of this scheme is that the disturbance is
compensated in the velocity loop and it is not necessary consider in the position loop. The advantage of the two- degree-of-freedom
control is that the characteristics of response to reference commands and the feedback characteristics can be designed independently.
Experimental results show good positioning accuracy.
Finally, the energy-saving effect of transformer is studied. In lifting systems, although the potential energy of load is recovered in
downward stroke, it is inadequate to estimate the energy-saving effect using only the energy recovery efficiency in downward stroke,
since the supply energy in upward stroke have to be considered. As the criterion, the non-dimension energy consumption in a cycle
including both upward and downward stroke is proposed.
Here, the load ratio is defined as the ratio of the load torque on steady state and the maximum theoretical torque of VDPM. Then
the higher the load ratio and setting pressure are, the better the energy-saving effect is. In circuit 1 where the VDPM exchanges energy
with the constant pressure supply, the load ratio affects the energy-saving effect greatly. When the load ratio is low, there is no
energy-saving effect because the VDPM is operated in low efficiency domain. In circuit 2 where both the VDPM and the FDPM
exchange energy with the constant pressure supply, the energy-saving effect is better in a wide range of load ratio. When the setting
pressure, the load ratio, and the circuit type are selected properly, the total output energy from the constant pressure supply in a cycle
can be half of the energy of upward stroke, and the energy-saving effect is acquired.
In recent years, there has been a growing awareness of the hazards of industrial noise and how to reduce it in hydraulic systems.
A great number of studies have been carried out in the past in this field and it has been shown that the source of these perturbations
has to be sought in the process of the generation of flow ripple as an intrinsic characteristic of the pump. As a consequence of this,
any advance in this field has to inevitably pass the simulation of the dynamic behaviour of the pump.
The investigation work presented in this thesis is concentrated on the performance analysis of a gerotor pump in order to develop
a coherent and unified global study of the trochoidal profiles geometry of the gear, the kinematics of the mesh, the volumetric characteristics,
the contact stress at the contact points and its fluid dynamic behaviour.
The geometry and kinematics of the mesh of the trochoidal gear has been analytically deduced through the equations of the teeth
profiles and the line of contact, which are in turn function of four basic parameters and were the basis for further studies.
The volumetric characteristics have been developed and compared by using two approaches: the integral-derivative approach solved by a
numerical differentiation and the derivative-integral approach solved by a numerical and analytical integration. The coherence of the
results obtained by both approaches is very satisfactory.
Contact stress calculation is also proposed and developed by using two methodologies. The first method is based on Colbourneís
theory and it is implemented by a new approach to the calculation of the contact points. This method is only valid for external gears
formed by circular-arc teeth. Because of the limitation of this method, an alternative and more generic method has been proposed by
implementing the Finite Element Method. This last method provides more reliable magnitude values of the maximum contact stress
and it has shown a high flexibility that aids the process of optimization of the teeth profiles geometry.
The fluid dynamic behaviour of the gerotor pump study is based on a physical simulation method (BondGraphís Method) which
is focused on the flow ripple calculation. The simulation model presents an analytical approach which starts with a submodel of a
single chamber and it is completed by the interaction of gear-pump and leakage flows. This numerical methodology is contrasted
with an experimental methodology (Secondary Source Method) which allows a direct comparison between results from both methodologies.
Two test rigs have been employed and developed according to the ISO normative 10767-192/84247: one of the test rigs is
at the Fluid Power Centre of the University of Bath and the other test rig is specifically designed and constructed for this thesis at the
LABON Centre. A comparison of the experimental results has shown that the amplitude (peak to peak) of the flow ripple of the Fluid
Power Centre is more accurate than those obtained at the LABSON Centre.
The comparison between the
This thesis deals with the development and investigation of advanced drive line control concepts for off-road vehicles to reduce
the power losses of the entire drive system by use of on-line optimization procedure. This finally allows reducing the fuel consumption
of the working machine. Different optimization strategies have been developed and theoretically and experimentally investigated
in this thesis. For the control concept two separate closed loop speed controls have been developed for the use on a microcontroller
onboard the vehicle: one to control the hydrostatic transmission and the other to control the engine speed. A direct optimization strategy,
working on-line on a microcontroller, is used, which considers the loss characteristics of both displacement machines of the
hydrostatic transmission as well as the steady state characteristics of the combustion engine using pure mathematical approximations
of measured curves. This control concept is especially suitable for off-road vehicles, where the drive line is an essential part of the
machine operation, when used for material transportation purpose.
A laboratory hardware-in-the loop test rig has been used to investigate the proposed control concepts for different basic system
concepts of drive lines using fixed displacement motors or using variable displacement motors. Whereas the hydrostatic transmission
has been installed on the test rig, the combustion engine has been simulated with the help of an electric motor. A secondary controlled
hydraulic motor has been used for load simulation, i.e. to simulate the vehicle including the wheel surface contact and the
vehicle inertia. For different typical and desired work cycles of an off-road machine on level ground and uphill a slope the effectiveness
of the proposed control concepts have been proven.
This thesis presents some recent developments of a research activity regarding hydraulically balanced external gear pumps and
motors. Numerical models have been developed and applied in order to study gears radial equilibrium and axial bearing blocks balance.
In particular, a numerical approach useful for determining the eccentric positions assumed by gears inside the pump casing and to
assess the radial thrusts acting on gears is proposed. The effect of the running in process on the casing internal surface and on the
pressure distribution in sealed spaces between teeth is presented and deeply discussed.
Then, a numerical model useful in designing bearing blocks balancing surfaces is outlined. In particular a second order finite difference
integration scheme is involved with the aim to solve the Reynolds equation inside the clearance bounded by gears sides and
bearing blocks internal surfaces. In this case, both constant and variable height clearances have been considered and investigated.
First of all, comparisons between numerical and experimental results permit to validate this methodology that has been successively
applied for designing the balancing surfaces of commercial gear pumps and motors bearing blocks.
The flow field inside the clearances bounded by gears lateral sides and bearing blocks internal surfaces of external gear pumps
and motors has also been studied. In this case, the pressure distribution is determined applying the Laplace equation to the domain
limited by two successive teeth profiles, the middle lines of the first and of the last space and the drain circle, and the main leakage
paths inside the clearance are evaluated. Then, the leakage flows between spaces, and between each space and the drain ambient, are
calculated considering different boundary conditions and teeth shapes, and the streamlines are highlighted in order to evidence the
main leakage paths. The information gathered through this flow field analysis are used to define equivalent conductance for leakage
paths, useful to be adopted in simple lumped parameters models, usually applied with the aim to determine the pressure distribution
inside pumps and motors casings or, for example, external gears units volumetric efficiency.
In the last part of the thesis the analysis of the inter-teeth pressure transients during gears meshing cycle of external gear pumps is
presented. In this case, a lumped parameter model, tailored for the prediction of pressures in the meshing zone, is firstly involved.
The numerical model, based on the integration of the continuity equation, is applied to the inter-teeth volumes, communicating with
the neighbouring ambient through geometry dependent orifices. A comparison between numerical results, obtained considering both
constant and variable discharge coefficients, is illustrated. Successively, the dependency of pressure transients on gear pump operating
conditions, mainly in terms of delivery pressure and rotational speed, is investigated. The effect of some geometric parameters is
also discussed, mainly considering different gears widths and interaxial distances, and high-pressure recess positioning. Finally, in
order to highlight the influence of the cavitation modelling on low pressure transition, the results coming from the application of two
simplified approaches are shown and compared.
In recent years, developments in mobile machines have to a considerable extent been concerned with improving energy utilization
and reducing power loss. High-efficiency drives have been applied on mobile machines. This study is focuses on the energy
utilization of hydraulic booms, which are very often used in mobile machines.
The study starts with a comparison of different solutions for the ER systems in mobile applications. It compares especially different
types of HAB system. System modeling and simulation of a hydraulic boom are carried out as a key part of the study. The sequence
of "modeling => experimental measuring => verifying model => simulating again" is the process followed in the whole
study.
A new type of Energy Regeneration (ER) unit using Hydraulic Accumulator Balancing (HAB) has been developed in this study.
The work of designing, modeling, implementing, and testing the HAB unit is presented in this thesis. The study concentrates on a
simulation study based on a verified model, which is calibrated by experiments. The simulation provides the conclusions regarding
energy-saving performance.
Various topics that are worth while developing further in the future have been discussed at the end. The topics are: defects of this
study, HAB type (F), additional energy saving (AES) valves, pressure feedback (PF) flow control, R&D for a more accurate model,
real-time simulation, and the system of secondary utilization of return oil (SUORO).
Finally, the summary and conclusions are presented.
In this study, we proposed using the slit structure instead of orifice structure to reduce the noise level and the pressure disturbance
in the pressure reducing system. The slit structure makes the flow laminar even if the upstream flow is turbulent flow and the
pressure ratio is lower than 0.528. The compressed fluid enter the center of the disk and is exhausted through slit with radial direction
from the inside region to outside. The height of slit is made small (about 0.05-0.1mm) using MEMS technology in order to make the
flow laminar. When the fluid flows through the slit, the fluid energy would get scattered and lost because of viscous resistance of
fluid. The noise reduction efficiency is investigated by some experiments. It is known that the slit structure reduces the noise level
about 40 [dB]. Finally, a new servo valve set in the slit structure was developed and confirmed its effectiveness.
By W. Borutzky
440 pages
Publisher: SCS Publishing House, Erlangen, San Diego
ISBN: 3-936150-33-8
Nowadays, engineering systems to be designed are of ever-increasing complexity and must be considered as multidisciplinary
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electrical and control engineering in a concurrent design approach is required. With regard to the modelling and the analysis of a
system, interdisciplinary methodologies become more and more important.
A graphical description formalism particularly suited for multidisciplinary systems are bond graphs devised by Professor Henry
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This book, written in English, addresses students, teachers, researchers, and practising engineers in academia and in industry who may have heard something about bond graphs and who want to learn more about the potential and the state-of-the-art of this exciting modelling methodology, in order to see how it can help them better understand physical processes and to develop good models in their engineering field. The book comes with an electronic version of the text on CD that makes use of colours and supports navigation by hyperlinks.