This thesis presents a solution enabling lower losses in hydraulic actuator systems. A mobile fluid power system often contains several different actuators supplied with a single load sensing pump. One of the main advantages is the need of only one system pump. This makes the fluid power system compact and cost-effective.
A hydraulic load often consists of two ports, e.g. motors and cylinders. Such loads have traditionally been controlled by a valve that controls these ports by one single control signal, namely the position of the spool in a control valve. In this kind of valve, the inlet (meter-in) and outlet (meter-out) orifices are mechanically connected. The mechanical connection makes the system robust and easy to control, at the same time as the system lacks flexibility. Some of the main drawbacks are:
1)  The fixed relation between the inlet and outlet orifices in most applications produce too much throttling at the outlet orifice under most operating conditions. This makes the system inefficient.
2)  The flow directions are fixed for a given spool position; therefore, no energy recuperation and/or regeneration ability is available.
In this thesis a novel system idea enabling, for example, recuperation and regeneration is presented. Recuperation is when flow is taken from a tank, pressurized by external loads, and then fed back into the pump line. Regeneration is when either cylinder cham-bers (or motor ports) are connected to the pump line. Only one system pump is needed. Pressure compensated (load independent), bidirectional, poppet valves are proposed and utilized.
The novel system presented in this thesis needs only a position sensor on each compensator spool. This simple sensor is also suit-able for identification of mode switches, e.g. between normal, differential and regenerative modes. Patent pending.
The balance of where to put the functionality (hardware and/or software) makes it possible to manoeuvre the system with main-tained speed control in the case of sensor failure. The main reason is that the novel system does not need pressure transducers for flow determination. Some features of the novel system:
1)  Mode switches The mode switches are accomplished without knowledge about the pressures in the system
2)  Throttle losses With the new system approach, choice of control and measure signals, the throttle losses at the control valves are reduced
3)  Smooth mode switches The system will switch to regenerative mode automatically in a smooth manner when possible
4)  Use energy stored in the loads The load, e.g. a cylinder, is able to be used as a pump when possible, enabling the system to re-cuperate overrun loads
The system and its components are described together with the control algorithms that enable energy efficient operation.  Meas-urements from a real application are also presented in the thesis.

    The main content of the thesis is the creation of mathematical model and simulation of dynamical properties of structure, which is called testing board with six degree of freedom. Testing board is a real testing device, which was developed and built on the TU Liberec. Theoretical part of the thesis is focused on problems with the mathematical modelling of larger structures with using of algorithms, which are generally called the reduction methods. Especially the algorithm called Craig-Bampton is described. The thesis contains two main sections. The first section is focused on the creation of model with finite element method utilization, using the software ANSYS. ANSYS was used for eigenfrequencies and eigenvectors computations. The second part is based on solutions of forced vibration analysis. Comparison between model only with rigid parts and the model with flexible parts is presented. This com-parison is used to clarify the effect of flexible parts on the movement of the inspected body by the excitation with deterministic and pseudo-stochastic signals. The Craig- Bampton algorithm is used for the transfer of flexible parts from ANSYS to ADAMS, which was used for vibration analysis. The experimental operation deflection shapes analysis (ODS) is also a part of this thesis. The com-parison between experimental and computed results is presented.

  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 au-thor 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 leak-age. 
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 leakage dominated the overall leakage from the pump, with piston leakage being insignificant. This model was also used to predict the flow and pressure ripple from the pump and the predictions were compared with measure-ments.

      This thesis presents the development of the first ever racing vehicle yaw control system that utilizes active dampers to provide a corrective yaw moment through the manipulation of tire contact patch loads during transient vehicle handling maneuvers. The study has focused on the following three key areas:
1) The design of a magneto-rheological (MR) damper
The damping requirements of a racing vehicle are investigated. A prototype magneto¬rheological damper is proposed and evalu-ated using magnetic finite element techniques. The manufactured prototype is subsequently tested and benchmarked against a passive racing damper and a commercially available MR damper. Consideration is given to the current driver circuit required, the damper response time to increasing and decreasing demand signals and sealing and bearing requirements.
2) A novel yaw damping strategy utilizing active MR dampers.
This work proposes a novel active damping strategy for vehicle yaw control. The dampers are used to control both the pitch and roll damping distribution during transient vehicle handling maneuvers. It is shown that this approach improves the functionality of previous damper based yaw control that only considered roll damping distribution.
3) In-Vehicle implementation and track testing
An in-vehicle damper control system is developed using hardware that has not previously been employed in this application. This study is the first to apply a damper based yaw control system to a racing vehicle. Track testing of the racing vehicle fitted with the damper control system is used to demonstrate the potential improvements achievable in the context of lap time, subjective driver feel and measured yaw error.

Because of physical and biological contamination, filtration may turn out to be problematic in water hydraulic systems. Contami-nation may quickly increase the pressure difference over the filter cartridge; consequently, this research aimed to test the depth type filter cartridge and to determine the effects of microbial growth and particulate contamination on filtration in a water hydraulic sys-tem. Experiments were run by using tap water with R2A as a biological contaminant and ISOMTD as a particle contaminant.
The contamination control of water hydraulic systems starts with the design of the system. Special features of water hydraulics must be taken into account while designing, because the best way to prevent problems caused by biological contamination is to build a system with minimum interface between pressure media and the surrounding environment. In addition, clean work practices during start-up and maintenance have long-term effects on the operation of the system.
        Particle contamination can be filtered without special applications, when the biological contamination level is low; but when mi-crobial growth has been induced, the best way of prolonging the system’s operation time is to increase the filtering area. In return lines, no smaller depth filters than that of pore size 10 µm needs to be used, because microbial growth improves their filtering capa-bility even at low growth levels.