PhD-Theses completed in 2008
Self Energizing Electro-Hydraulic Brake
Institute for Fluid Power Drives and Controls (IFAS)
Aachen University (RWTH) Aachen, Germany
This thesis presents research results on a new fluid-mechatronic brake
principle. The Self-energizing Electro-Hydraulic Brake (SEHB) utilizes
the effect of instable self-reinforcement in combination with a closed
loop control. Background for the development of the brake concept is a
train application. However, SEHB is not limited to any specific
application. Main advantages of the concept are its minimal energy
consumption, the closed loop control of the true brake torque and its
feedback ability due to the decentralized low-power electronic
control.
This thesis introduces the new brake principle by comparing it to
conventional self-reinforcing brakes. A mathematical distinction is
given between self-reinforcement and self-energization on the basis of
static considerations. The dynamic characteristics are analyzed using a
linearized system description which is further simplified using the
method of pole dominance analysis. The simplified model is used to
calculate a state dependent proportional controller map on the basis of
damping criteria. Besides the theoretic analysis, the thesis presents
the basic hydraulic design criteria and gives a systematic overview
over different hydraulic-mechanical design solutions. A special focus
is given on the valve control, since it is vital for the brake
performance. Different automotive valves such as from antilock brake
systems (ABS) or electronic stabilization programs (ESP) are applied
using electronic power switches and current drivers. The brake test
stand and two successive prototypes are outlined at the end of this
thesis. Different exemplary measurement results show the performance of
the implemented types of valve control and demonstrate the potential of
this new brake technology.
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Torsten Kohmaescher
Modeling, Analysis and Design of Hydrostatic Drive Line Concepts
Institute for Fluid Power Drives and Controls (IFAS)
Aachen University (RWTH) Aachen, Germany
Energy requirements for off-highway machines, e.g. wheel loader of 120
kW engine power, are determined by numerous load cycles. Fuel
consumption of the machine results furthermore from the interaction of
hardware (diesel engine and transmission) and software (transmission
control unit) in the drive train concept. Utilization of continuous
variable transmissions (CVT), e.g. hydrostatic transmissions or
hydro-mechanical power split transmissions, decouples engine speed and
vehicle velocity and therefore enables an additional degree of freedom.
Hydro-mechanical power split transmissions combine continuous
variability of hydrostatic transmissions and high efficiency of
mechanical transmissions. For evaluation of functionality, power flows,
losses and fuel consumption system simulation is a suitable tool for
design engineers. The applied simulation models have to be capable of
modeling the complex loss behavior close to reality.
These losses are not only determined by the transmission itself but
also and in particular by the diesel engine and the transmission
control unit. This thesis contributes to the evaluation of the
application potential of various simulation approaches for the
simulation of hydrostatic drive line concepts. Modeling is not only
considering detailed losses in hydrostatic pumps and motors but is
additionally calculating the losses caused by mechanical transmission
components. The mechanical losses are calculated according to empiric
equations. Losses in hydrostatic units are implemented in the
simulation by means of special loss modeling methods which are
evaluated in scope of this thesis.
The focus is on the systematic as well as on the modeling of
hydro-mechanical power split transmissions. Three different approaches
for the investigation of drive line concepts are introduced. By this
means characteristic curves and maps can be generated as well as
frequency distributions of operation conditions (pressure, speed,
displacement) of the interacting components (pumps, motors, planetary
drives) during load cycles. By the experimental verification of the
simulated results significance of the simulation approaches is
increased. As a concluding example the cycle-based simulations are
applied for the development of a 3-stage power split transmission. The
three stages of the transmission utilize the three different basic
concepts of power split transmission.
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Active Valve and Pump Technology: Modelling and Control of Variable-Speed Trim Transfer Pumps in Aircraft Fuel
Systems
Center for Power Transmission and Motion Control
University of Bath, Bath, UK
The
current generation of Airbus long-range civil transport aircraft
actively control the centre of gravity of the aircraft by adjusting the
fuel distribution between the horizontal tail surface and the forward
tanks in order to minimize cruise drag. Here, it is proposed that the
current on-off control method could be replaced by a variable flow
rate, provided by a variable speed centrifugal pump. The impacts of
this at the aircraft level in terms of cruise fuel burn reduction,
valve operation cycle reduction and power consumption are investigated
here using an extension to an existing fuel system simulation package
and a generic aircraft fuel system definition. It is shown that using
such a control system reduces fuel burn and the number of valve cycles,
which could translate into a reduction in operating costs. The benefit
of changing the controller to use tailplane trim angle directly rather
than inferred centre of gravity position is assessed, and is shown to
further reduce the fuel burn. It is suggested that such centre of
gravity could provide significant benefits over the existing method.
Steady-state and dynamic models of centrifugal pumps, AC induction
drives and typical aircraft fuel system pipework components are
developed. These are validated against experimental data from a test
rig of a representative system. Test rig simulation results are shown
to agree well with those from experimentation. A new secondary noise
source is developed for the dynamic analysis of the centrifugal pump,
and a new acoustic experimental method is developed for the prediction
of fluid inductance in pipework components. The results are compared
against an existing CFD based method and show good agreement. The new
method represents a much simpler experimental means of determining the
effects of fluid inertia than the existing secondary source method. It
is demonstrated that the dynamic behaviour of the centrifugal pump is
insignificant when considering systems containing long pipes, and that
steady-state pump models are sufficient for analysing their behaviour.
The pump models are generalised by non-dimensionalisation, in order to
maximize their applicability to analysis of aircraft fuel systems. They
are applied to a generic aircraft fuel system simulation, in order to
model the behaviour of the system during a trim transfer. This is used
to demonstrate the application of the proposed variable flow rate trim
control system. The results of these simulations agree well with those
used to demonstrate the benefits of the control system at the aircraft
level. Concepts of system health monitoring tools are discussed with
reference to the system simulations.
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Active Control of Fluid-Borne Noise
Center for Power Transmission and Motion Control
University of Bath, Bath, UK
Fluid-borne
noise is one of the main components of hydraulic noise. The attenuation
of it may have a significant effect on the cost in hydraulic systems.
Standard passive silencers and dampers can be useful in reducing it in
certain frequency ranges; however, these tend to be heavy, bulky and
expensive. Active control algorithms, which are a comparatively recent
means to reduce fluidborne noise, can be applied to overcome this
compromise.
The work presented in this thesis is the development of some active
control algorithms utilised in a simple hydraulic system to cancel a
number of harmonic orders of fluid-borne noise generated by a servo
valve or a real pump. To realise cancellation, the filtered reference
least mean square (FXLMS) adaptive control method is mainly
presented. Furthermore, a fast response servo valve is applied as
an actuator to generate a proper anti-noise flow signal in real time.
For simplicity, an off-line identification method for the secondary
path is applied in the time invariant working condition. Moreover,
ripple reflection from both ends of the hydraulic circuit can give
different effects under different working conditions. In order to
execute the cancellation without any priori information about the
dynamics of hydraulic system, the on-line secondary path identification
method is discussed. However, in this algorithm an auxiliary
white-noise signal applied for on-line method may contribute to
residual noise and an extra computation burden can be added to the
whole control system.
The performance of these control algorithms is firstly investigated via
simulation in a hydraulic pipe model and the real time application on
test rig using a servo valve as noise source. Finally, these schemes
are realised in a simple hydraulic system with real pump noise source.
The fluid-borne noise can be attenuated by about 20 dB with normal
working conditions.
A New Approach for Numerical Simulation of Fluid Power Circuits Using Rosenbrock Methods
Department of Intelligent Hydraulics and Automation
Tampere University of Technology, Tampere, Finland
Because
of the intrinsic characteristics and physics of fluid power circuits,
the numerical integrators employed to solve the dynamic equations
describing such systems must retain certain properties in order to
guarantee the accuracy, stability and efficiency of the numerical
integration and its solution. In his thesis the author proposes a
modelling approach which takes advantage of Rosenbrock integration
methods. The only drawback of Rosenbrock methods is that a numerical
evaluation of the Jacobian has to be pro-
vided at each integration step. With the presented modelling approach,
the analytical form of the Jacobian matrix is formed automatically for
any given system. Its numerical evaluation at each integration step
provides a cheap and yet accurate Jacobian to the Rosenbrock formula.
This makes Rosenbrock formulas (so far not extensively used in fluid
power applications) to show excellent numerical stability properties
and also above-the-average efficiency (solution accuracy to number of
integration steps ratio). The tests pre
sented in this thesis have confirmed that Rosenbrock formulas are good
candidates for being used in real-time simulations (fixed integration
step size) and in offline simulations (variable integration step size)
of fluid power circuits. Their easy implementation, good stability,
high efficiency and low computational costs make them, in most of the
cases tested, superior to other popular codes.
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Contribution to the characterization of flow in pneumatic components based on tank discharge
Institut National des Sciences Appliquées de Lyon
Lyon, France
This PhD dissertation is in line with the problematic concerning
the modelling and the characterization of pneumatic components and
circuits. The present standard for mass flow rate characterization (ISO
6358) leads to an important consumption of energy since it is based on
measurements in stationary flow conditions. To compensate the time and
energy cost of the existing method, a novel procedure based on the
discharge of specific "isothermal" tanks was proposed by the Tokyo
Institute of Technology.
The originality of our research work is to propose a new approach based
on the computation of the mass flow rate from the inversion of the
dynamic behaviour model of a pneumatic chamber. Applying this approach
to the discharge of an ordinary tank through the component to be
characterized, it enables the mass flow rate characteristics to be
directly determined from the measurement of the transient pressure in
the tank and the computation of its time derivative. The study of the
implementation of a rig for mass flow rate characterization based on
the discharge of an ordinary tank requires then a various engineering
knowledge in fluid mechanics, thermodynamics, and applied mathematics
that are given in the dissertation.
One of the main contributions of this work aims specifically at the
introduction of a macroscopic model of the heat transfer at the wall of
a tank when discharging. Based on dimensional analysis, this model
avoids the measure of the temperature in transient conditions to
determine at any time the gas state, this being one of the main
difficulties in pneumatic systems. In addition, these theoretical
developments rely on a wide experimental work. It has allowed the
validation of the flow characterization method and also of the heat
transfer model. For this last one, its ease of implementation suggests
potential uses for various industrial applications.
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Model Based Development on the Example of Pilot Operated Pressure Relief Valves
Institut für Fluidtechnik der TU Dresden
Technical University of Dresden, Dresden, Germany
Electrohydraulic
valve systems are important components in modern fluid power
applications. Because of the increasing requirements on functionality,
robustness and sound emission, the use of conventional methods in
product development causes a lot of effort regarding time and costs.
The mechatronic properties of the valves are characterised by the use
of electric, electromagnetic, mechanical and fluid mechanical
disciplines. The specific tuning and optimization of those subsystems
requires a holistic development approach in order to reduce
experimental development time.
The thesis is dealing with a model based development approach with
regard to a holistic development of electrohydraulic valve systems.
Therefore typical valve systems are analyzed in terms of fields of
applications for different simulation methods. A special focus lies on
the use of CFD- or FEM-methods. As one of the most important subsystems
of a valve, the proportional solenoid is particularly investigated by a
FEM-model. Based on the result of FEM, a reluctance network is
developed and parameterized. So the proportional solenoid can be used
in a holistic lumped parameter model without doing any experimental
work for parameterization. The spool edges affect the whole valve
performance as well. The equations to describe hydraulic resistances or
flow forces are well known. In order to avoid experimental parameter
estimation, a new way is shown to determine model parameters by using
simplified CFD analyses. Two examples are used to demonstrate the value
of virtual prototypes in order to be used in the valve development
process. Therefore a stability problem is solved by using a linearized
model. The second example describes a way to design valve electronics
for compensation of the valve nonlinearities by using the virtual
prototype.
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Awards in 2008
Outstanding teacher in the Agricultural and Biological Engineering
Department at Purdue University and nominated for the Potter Engineering Award.
Awarded to
Prof. Gary Krutz P.E.
Purdue University, West Lafayette, IN, USA
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