Andreas Bootz

During the past years the market for steering-systems has changed dramatically. Many car models with conventional mechanical or hydraulic assisted power-steering-systems were equipped with new electro-hydraulic or electro-mechanical steering-systems.
The reason for these efforts - besides the desire for more comfortable driving - is the aim to reduce fuel consumption and in-crease the functionality of steering-systems. However, an increasing number of functional degrees of freedom requires a higher steer-ing power demand, which - especially in heavy vehicles - can not be fulfilled with electrically driven systems.
In this thesis, the electro hydraulic Closed-Center-steering-system (CC) is investigated as an alternative to electrically driven steering-systems and conventional hydraulic Open-Center-steering-systems (OC) for the use in passenger cars. The crucial criteria are the maximum amplitude, the time response and the mean value of power consumption.
To understand the working principles of the conventional OC-steering-system and the CC-steering-system a system description is provided. Several alternatives for a hydraulic power supply unit are introduced and analysed. Control strategies for ensuring a con-stant system pressure are discussed.
In order to simulate the power consumption of both steering-systems the appropriate model approaches are developed - including a model for simulation of the wheel loads. Further input quantities of steering-systems are described by driving cycles containing defined steering movements, which allow the calculation and experimental investigation under realistic conditions.
With the help of the developed models, the different alternatives for the pressure supply unit are examined and rated according to specific criteria. As the best concept, the suction controlled radial piston pump is chosen for further experimental investigations of the CC-steering-system.
Using measurements of characteristic quantities of the radial piston pump, the existing simulation models are refined to allow a precise forecast of the power consumption of the steering-system. The final assessment of the measurement and simulation results shows that in comparison to conventional hydraulic steering-systems the CC-steering-system allows a significant reduction of power consumption.

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Albert Raneda

This thesis presents the novel research contributions on the feasibility study of a water hydraulic drive for position and torque control, the implementation of an impedance control scheme to handle the interaction between a manipulator and the environment, and the development of an efficient model-based teleoperation application. The suitability of a water hydraulic drive for teleoperation applications is studied by analyzing the behavior of a rotary vane actuator with different control configurations such as position, torque, and impedance control schemes, and using pressure transducers or a force sensor to estimate contact forces.
A model-based teleoperation approach is implemented to handle the interaction between the operator and the telemanipulator. Model-based teleoperation uses virtual reality techniques to augment the human-machine interface to assist the operator. The use of model-based teleoperation for the operator-telemanipulator interaction, together with the impedance control scheme to regulate con-tact forces with the environment and with water hydraulic technology, makes it possible to implement a teleoperation system capable of dealing with the demanding task requirements occurring in remote and hazardous environments.
Simulation and experimental results are presented, showing the effectiveness of the implemented teleoperation system.

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Bernd Winkler

The improvement of working processes for increased productivity is one of the major tasks of the technical development in agri-cultural machinery. Therefore, besides other measures the working velocity and quality of work have to be increased. Mechanical distance devices in grass harvesting machines, such as simple wheels, rollers or vats meet their mechanical load capacity at operating speeds of 20 km/h and more. A further shortcoming of such common devices which are based on mechanical contact is the damage of soil or sod. Thus, an automatic level control unit is a key technology to achieve the mentioned improvements like higher working velocities and increased quality of work. The wheels of the pick-up are now replaced by two hydraulic cylinders and appropriate hydraulic valves, which are guiding the pick-up in an appropriate distance over the ground. The distance to ground is measured by ultrasonic sensors. With this signal and the actual position of the hydraulic cylinders a micro-controller controls the pick-up position via proportional valves. Via the ISO-bus system the operator can adjust certain parameters. The system has to respond on obstacles appearing during full working velocity. This means that the 250 kg pick-up has to be lifted within 200 ms (0.2 s) from its lower to its upper position. To provide the required forces relatively big hydraulic cylinders and valves, the latter with a short response time, are needed. We developed a fast low cost switching valve for high flow rates. The result of this development is a switching valve which switches within 1ms a flow rate of up to 100 l/min at 5 bar pressure drop (20 times faster than comparable commercially available valves). The valve has the potential to production costs of about 50 € in a full production run.

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Norbert Krimbacher

A novel principle for a switching type hydraulic actuator for energy saving fast positioning is investigated. The design goals are short switching times, high robustness and low energy consumption. The considered switching times are in the order of milliseconds, the moved masses m are between m = 5...1000 g and the stroke xmax of the movement is about xmax = 0.5...20 mm. Fast positioning of hydraulic steering elements of high flow hydraulic valves is a necessity to implement energy efficient switching techniques for hy-draulic systems. There switching frequencies of about 1 kHz and flow rates of up to 250 l/min are intended.
General aspects of fast positioning are presented and a glance on state of the art actuation of hydraulic valves is shown. Addition-ally, some novel actuation principles for specific applications are described. Energy aspects on fast positioning are discussed after-wards.
The novel principle is discussed and several analytical models are derived to point out interrelationships between various design parameters. To get a greater insight into the systems behaviour theses models are refined and numerical studies are carried out.
This novel fast positioning concept is realised to build up a Fully Variable Valve Train for combustion engines. The inlet- and the outlet valves of such engines have to be opened and closed within short times between two definite positions. Process forces due to the pressure of the combusted gas have to be considered and have to be compensated. A test rig was designed, manufactured and successfully tested. Second, the basic concept is modified to realise high speed switching actuators. The changed parts of the basic concept are dis-cussed, the hydraulic scheme is shown, analytical models are derived and numerical simulations are run. A prototype was designed and tested. This prototype is designed as a modifiable actuator which can drive several units, e. g. standard hydraulic sliding valves or safety valves. There short switching times and high reliability are necessary to achieve correct performance.

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