On valve controlled fluid power systems : flow amplifier and percussive rock drilling

Sammanfattning: This thesis discusses how the design of hydraulic systems and components can be made to meet the demands of a future market in terms of efficiency, flexibility and cost. It also discusses how computer simulation can support the designer to get a higher knowledge of the system and to make the design phase more efficient.These tasks are discussed in the two main parts of the thesis:• A simulation study of a reciprocating rock drill machine. • The development of a high response two-port control valve, developed within this thesis work, called the Twin Valvistor.Although the two parts exhibit several differences, both in focus and in design and control, there arc key similarities combining them. They both concern applications where valves arc used as the control clement and the main state is controlled with some type of feedback of the state controlled.The reciprocating rock drill represents a switched motion control, where the direction of the acceleration of the drill hammer is controlled. In this part, the focus is on the modelling of the total system. The aim has been to design a model with an equal level of approximation of all subsystems, a model that can be used in the tuning of the machine and the control. Due to the importance of the energy transport between the drill hammer and the rod, the main part of the work concerns the modelling of stress waves in the drill rod and the impact between the hammer and the adapter connected to the rod. The aim of the work about the Twin Valvistor has been to develop a robust and inexpensive valve that offers a high flexibility and generality. The Valvistor is a seat valve with a hydro-mechanical position control of the valve piston. The thesis also discusses ways to improve the stability and stiffness to load disturbances of this design. Possible applications and control strategics for the Twin Valvistor have also been investigated, with a focus on pressure control.