PhD-Theses completed in 2008
Self-energizing Electro-Hydraulic Brake
Institute for Fluid Power Drives and Controls (IFAS)
RWTH Aachen University, 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 areanalyzed 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 a 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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Menggeng Yang
Modelling and analysis of pressure pulsations in hydraulic
components
and systems with particular reference to pump fault diagnosis
Department of Mechanical Engineering
University of Bath, Bath, UK
Vane pumps are simple in principle and can be mass produced
inexpensively, making them well suited to the automotive industry. They
also have many other applications, such as in the chemical industry and
food industry. A common type of damage to a vane pump is cavitation
erosion on the side plates. If this damage is not detected in time, it
could cause failure of the pump, which depending on the type of system
may have safety implications, and in some cases a high cost from lost
production whilst the system is shut down. This kind of damage is
common on other types of pumps such as gear pumps and piston pumps. So
a practical method for fault diagnosis of hydraulic pumps is required
which does not necessitate removal of a pump from the working system.
This thesis presents a method of
detecting and identifying cavitation damage on vane pump side plates
via pump flow ripple. Power steering vane pumps are used for this
study, although the principles may also be applicable to other types of
vane pump, and indeed to piston and gear pumps. The investigation has
been done through measurement and simulation. A numerical model of a
vane pump is described, and simulated cavitation damage is introduced
into the model. This damage is shown to have a clear effect on the
simulated flow ripple. The pump flow ripple has also been measured
experimentally using the Secondary Source Method, and artificial damage
has been introduced into the pump. The damage is shown to have a clear
effect on the measured flow ripple, consistent with the simulation
results.
Whilst the secondary source method
enables the measurement of flow ripple in laboratory conditions, it is
generally impracticable for in-situ measurement for condition
monitoring. Therefore the Deduced Flow Method (DFM) was developed to
determine the pump flow ripple. The method achieved good sensitivity
and accuracy for identifying cavitation damage in vane pumps using just
one pressure transducer and one optical trigger sensor.
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Study on the Speed Control of the Variable-speed Controlled
Closed-circuit Hydraulic Elevators
The State Key Laboratory of Fluid Power Transmission and
Control
Zhejiang University, Hangzhou, China
The behavior of the variable-speed controlled hydrostatic system was
investigated on a hydraulic elevator test rig in this thesis. To
achieve high precision control of the velocity, the stability of the
system was analyzed. Because the hydraulic elevator is a type 0 system
with the feature of low frequency, the steady-state error of velocity
still existed by unity-feedback control without compensation, and the
velocity lag occurred with the integral compensation. A compound
algorithm of PD & feedforward-feedback control was proposed to
deal with the steady-state error. To overcome the hysteresis in the
speed startup control of hydraulic elevator, the speed startup method,
based on expert control and model predictive strategy was developed,
and was validated by the experiments under different working
conditions. In addition, the vibration characteristics of the hydraulic
elevator were analyzed. The dynamic model with 8 degrees-of-freedom was
established for describing the vertical dynamics of the hydraulic
elevator system. The results of theoretical and experimental modal
analysis on the system showed the validity of the dynamic model. Based
on the requirement of
higher efficiency in hydraulic lift equipment, an innovative idea of
variable counterweight was developed. Compared with other
variable-speed controlled hydraulic systems, the efficiency of the
variable counterweight system was higher.
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Study on Flow Ripple and Valve Plate Optimization of Axial
Piston Pump
The State Key Laboratory of Fluid Power Transmission and
Control
Zhejiang University, Hangzhou, China
The mathematical model of flow characteristics
from piston pump was developed with distributed-parameter method. The
calculated results at pump discharge port using this model are more
accurate than those using lumped-parameter models in pressure pulsation
analysis. The influences of working pressure and temperature on fluid
bulk modulus were examined by experimental results to improve the
accuracy of simulation. Three-dimension (3D) dynamic simulation was
adapted using compressible fluid model to obtain the flow field within
the piston pump body. It was shown in simulation that the flow ripple
rate of piston pump increased from 5.8% to 17.8% at the same boundary
conditions, as a comparison with the experimental result of 18.6%. Thus
the simulation accuracy has been significantly improved using the
developed compressible fluid model. It can be seen from simulation
study that the compression ripple is the main part of flow ripple which
accounts to 88% of the total. The remainder leakage flow ripple has the
lowest proportion of 4%, and geometrical flow ripple takes the rest of
8%. Based upon the theoretical and experimental analysis, the
optimization ranges of the valve plate structure were proposed, which
could be used as a reference to design low noise level piston pump.
Lubrication
Characteristics and Parameter Optimization of
Plane Block-Port Plate Pair in Axial Piston Pump
The State Key Laboratory of Fluid Power Transmission and Control
Zhejiang University, Hangzhou, China
As its great importance and complicated mechanism, the oil film within
the barrel-port plate in axial piston pump was investigated in this
thesis. An algorithm was developed for the film configuration of port
plate, in which a set of experimental values of film thickness replaced
the corresponding node values in numerical method for solving the fluid
film equations. A new mathematical model using the wedge oil film was
developed. In this model, barrel tilting and port plate structure are
considered in the gap laminar flow. It was shown in the comparison of
calculated and measured results under different structure and operating
conditions that the barrel-port plate leakage rate was accounted for
about 35 % of the total leakage with 20 μm of film thickness.
When the film thickness was maintained within 5~15 μm, it may be
used as an optimal range for the barrel-port plate gap. In addition,
one parameter constraint of the lubricating oil film has been
implemented in the geometry optimization for the barrel-port plate.
Moreover, theoretical calculation of the tribo-pair can reduce leakage
rate and increase stiffness lubrication film within this tribo-pair,
which is helpful to improve the volumetric efficiency and lifecycle of
axial piston pump.
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Study on Oil Bulk Modulus and Temperature and Pressure Control
in Hydraulic Source with High Flow
The State Key Laboratory of Fluid Power Transmission and
Control
Zhejiang University, Hangzhou, China
The researches have been done on the
motion simulator for a docking mechanism comprehensive test-rig which
has an electrohydraulic servo system required high flow and high
performance. To improve the test accuracy, an installation was invented
and discussed according to the definition of oil bulk modulus, in which
information of pressure and displacement was directly extracted from
test chamber. The measurement accuracy reached as high as 3% because
the approaches were effective. Using this measurement device,
experiments were carried out on bulk modulus of hydraulic oil and a set
of values of oil bulk modulus with different air contents were made for
the first time. On account of characters of time delay and time-varying
parameters in oil temperature control, a set of control method was
proposed. The proportional water valve was used to control the flow
rate of cooling water and the parameter self-tuning fuzzy PID control
algorithm was used to control the opening of the valve. The simulation
and experiment results indicated oil temperature maintaining in
45±1. The study of steady-state and dynamic properties of
large-bore pressure control cartridge valve identified the rules of
performance changing with structure parameters.
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Exoskeleton based man-machine intelligent system and its
application
The State Key Laboratory of Fluid Power Transmission and Control
Zhejiang University, Hangzhou, China
The work of this paper is to provide a comprehensive
discussion of the exoskeleton-type system on the viewpoint of
manmachine system. The wear ability is the main characteristic of the
exoskeleton-type system. Its structure of exoskeleton should be
anthropomorphic and ergonomic, not only in shape but also in function
and in the distribution of the DOF as well. Basically, the control
architecture of exoskeleton-type systems is quite different from the
traditional intelligent robotics. In this control architecture, the
human operator is not only the commander or the supervisor of the
system, but also a part in the control loop, called
‘man-in-theloop’. By the successful implementation
of these two different kinds of exoskeleton-type systems, namely
exoskeleton arm for robot tele-operation with force-feedback and
lower-limb rehabilitation exoskeleton for post-stroke patients, the
basic principle of the biomechanical design and theory of the system
control were verified. Additionally, the experiments for their
applications were carried out. The work introduced in this paper has
significance for the future work on developing the exoskeleton-type
systems.
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Numerical simulation and experimental research on the working
process of
hybrid compressed-air and fuel engine
The State Key Laboratory of Fluid Power Transmission and Control
Zhejiang University, Hangzhou, China
A new hybrid compressed-air and fuel engine concept is proposed, which
can work by compressed-air powered engine mode and internal-combustion
engine mode. Although the hybrid engine is not zero pollution
emissions, fuel consumption and harmful emissions greatly reduce,
belongs to low-emission and fuel-saving engine. The main achievements
include the contents as follow. The series structure and the parallel
structure of hybrid compressed-air and fuel engine are designed, and
their operating principles and characteristic are respectively
elaborated. By the first law of thermodynamics and the second law of
thermodynamics, the working process mathematical model and the energy
analysis mathematical model of the two working modes of hybrid
four-stroke compressed- air and fuel engine are respectively
established. The working characteristics and the energy distribution of
the two working modes of hybrid four-stroke compressed-air and fuel
engine are researched using simulation computational method, and the
speed scope to switch the two operating modes is also analyzed. The
bench test of parallel two-stroke hybrid compressed-air and fuel
prototype engine is finished, and the switching rotation speed of the
two working modes is analyzed.
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Study on Dynamic Characteristics of a Valve-less Micropump
Accompanying Gas Bubbles and Cavitation
School of Mechanical and Electrical Engineering
Harbin Institute of Technology, Harbin, China
Being as an essential
component in micro-fluid control systems, a piezoelectric valve-less
nozzle/diffuser micropump can transport micro flow rate accurately. Its
application is getting wider and wider in micro electro-mechanical
systems, medical devices and biochemical engineering areas due to the
advantages of small size, simple construction and relatively high
responding speed. The appearance of gas bubbles and cavitation in a
micropump is generally undesirable as they can lead to performance
deterioration, life reduction and even complete failure of the pump. It
has been a key problem for the valve-less micropump. Therefore, it is
necessary to study the dynamic characteristics of valve-less micropump
accompanying gas bubbles and cavitation. According to the principle of
fluid dynamics and generation mechanism of gas bubbles and cavitation
in liquid, the dynamic mathematical models of the valve-less micropump
accompanying gas bubbles and cavitation are studied. Based on the gas
re-solution and releasing physical procedure, the models of gas bubble
and cavitation volumes are developed. On the basis of the cone tube
characteristics, the flow rate equations and the resistance
coefficients of the nozzle and diffuser are presented, respectively.
During pressure pulsation transients in a strait hydraulic pipeline
accompanying gas bubbles and cavitation, the mathematical models of gas
bubbles and cavitation are validated. The models of pressure transients
accompanying gas bubbles and cavitation, including basic equations and
friction items, are presented. Using finite difference method, the
transients in hydraulic pipeline accompanying gas bubbles and
cavitation are simulated. Two piezoelectric pressure transducers,
fitted to the pipe at different locations, are used to record pressure
transients. The growing and collapsing of gas bubbles and cavitation
are recorded using a high speed video camera. Therefore, the validity
of the gas bubbles and cavitation model is verified.
The model of gas bubble involves three
unknown parameters, including the initial gas bubble volume Vib, gas
re-solution time constant τin and gas releasing time constant
τout. By making use of genetic algorithms (GAs), the parameters
in the gas bubble mathematical model are identified by comparing the
pipeline transient simulation results and experimental data. Gas bubble
model, accompanying the pipeline pressure transients, with identified
parameters from GAs is obtained.
Based on the valve-less micropump
dynamic mathematical model, the dynamic characteristics of micropump
accompanying growth and collapse of cavitation and re-solution and
releasing of gas bubble is simulated. The influence of different cone
tube geometry, chamber size, vibration amplitude and frequency, as well
as the initial gas bubble volume on the micropump dynamic
characteristics are analyzed, including chamber pressure, outlet flow
rate, outlet accumulated flow rate, cavitation volume and gas bubble
volume. Using finite element analysis, the diaphragm maximum volumetric
deflection, stiffness and natural frequency are calculated.
The experiments of the piezoelectric
valve-less nozzle/diffuser micropump are carried out, including the
micropump performance test, dynamic test of pressure pulsations in the
pump chamber and the observation of gas bubbles. Meanwhile, the
modified model for the diaphragm maximum volumetric deflection is
presented. The micropump performance test includes outlet accumulated
flow rate and back pressure test. A piezo-resistive micro pressure
transducer fitted on the top of the chamber is used to measure the
pressure pulsations in the micropump chamber. In order to validate the
mathematical model and the simulation method, the actions of gas
bubbles, including movement, separation and combination in the chamber,
are recorded by a high speed video camera.
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Books & Proceedings Published in 2009
ISBN 978-83-7193-356-1
The dissertation deals with theoretical analysis and simulation of the
hydrostatic relief in the cylinder block-valve plate interface in the
axial piston pump. Three construction types of the valve plate: the
positive displacement type, zero displacement type, and the type with
relief grooves are discussed.
Given the dimensions and operating
parameters of an axial piston pump, the analytic models developed make
it possible to determine the trajectory of the resultant
pressing/relieving force, to determine the degree of unbalance between
the resultant hydrostatic pressing and relieving forces as function of
the cylinder block rotation angle as well as determine the unbalance of
the forces moments. The analytical model of the spatial piston load
provides the possibility of assessing the influence of friction force
occurring between the piston and cylinder to the hydrostatic load of
the cylinder block. The functional variation and the averaged leak flow
intensity is presented for the main pressure zone and in the upper and
lower transition zones as function of the cylinder block rotation angle.
The analytical models offered in the
present work and their implications can be applied for the designing of
axial piston pumps.
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