The improvement of working processes for increased productivity is one of the major tasks of the technical development in agricultural 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 20km/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 250kg pick-up has to be lifted within 200ms (0.2s) 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 100l/min at 5bar 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.

Magneto-rheological (MR) fluids are suspensions of micron-sized ferromagnetic particles in a non-magnetic carrier fluid. The essential characteristic behaviour is the rapid and reversible transition from the state of a Newtonian-like fluid to the behaviour of a stiff semi-solid by applying a magnetic field of about 0.1-0.4 Tesla. This feature, called the magneto-rheological (MR)-effect, can be understood from the fact that the particles form chain-like structures aligned in field direction. The MR-fluid offers three modes of operation. Either the direct shear motion of two magnetic poles separated by the fluid generates shear forces, or the valve mode restricts the flow through passages. Due to its highly non-linear behaviour, the third mode of operation, the squeeze mode, is up to now used for small amplitude vibration damping only. A test rig for the exploration of the MR-fluid behaviour was designed for experimental purposes. Special emphasis was put on the dependence of the MR-fluid response with respect to parameter variations of the applied static magnetic field, the cyclic loading amplitude and frequency values. Further, the cavitation phenomenon was investigated. Several attempts to describe the squeeze mode phenomenon with Finite Element simulations using different material laws such as a rigid-viscoplastic material law, an overstress power law and extended Drucker Prager models are presented. Thereby attained new perceptions gave reason to design an adaptive magneto-rheological fluid bearing in squeeze mode behaviour for industrial applications. A modification of the existing test rig was accomplished to prove the expected behaviour and benefits of this new concept. The substantial innovation is the rapid control of the radial load carrying capacity using the electric current as control variable. Furthermore, high load carrying capacities at low rotational speed can be accomplished whereby rate dependence is negligible. Particularly for the bearing in squeeze-mode, the interrelationship of the radial force and the magnetic flux induction as well as the squeeze gap geometry is of great relevance. For design engineering, preferably simple analytical approaches describing the load carrying capacity of such a bearing are of interest and are discussed in this thesis including a virtual power law with a von Mises yield law and a Levi-Mises flow rule. A promising industrial application of the magneto-rheological fluid bearing in squeeze mode can be found in the field of rolling technologies. The potential of usage is as a fully dynamic actuator capable of correcting, for instance, flatness defects of the strip. The application is studied by an example and by some design principles. Restrictions and problems of the application of MR-fluids are discussed, statements and ideas for further work necessary for a final industrial application are presented. Furthermore, a patent of the magneto-rheological fluid bearing in squeeze mode was successfully applied and published and is presented in this work. DOWNLOAD: http://imh.jku.at/publications/MR_Fluid_Applications_in_Squeeze_Mode.pdf

In this work a new displacement controlled linear actuator technology for mobile machines and robots working hydraulics based on differential cylinder is investigated. The new actuator concept uses a constant low pressure source and two pilot operated check valves for the compensation of the unequal cylinder flow rates. Great advantages according to the component expenditure and a strong system simplification are obtained with this new actuator concept, especially when several linear drives with differential cylinder or other drives like a hydrostatic transmission are coupled on the low pressure side. This new displacement controlled linear actuator type can work in open and closed control loop and allows a complex automatic machine working hydraulics motion control. Robust position and velocity control strategies based on LQG/LTR method are described. Furthermore, a quasi integrator prevents effects like limit cycles or wind-up. Measurement results with today’s standard control hardware prove the functionality of this actuator. The energy saving potential mainly due to recovery of load and brake energy and thermal behaviour of the new actuator type is analysed with the help of a precise mathematical model and typical mobile machine working cycles.