Hydraulic systems represent a crucial part of the drivetrain of mobile machines. The most important drivers of current developments, increasing energy efficiency and productivity, are leading to certain trends in technology. On a subsystem level, working hydraulics are utilizing effects by improving control functions and by maximum usage of energy recovery potential. Independent metering and displacement control, partly in combination with hybrid concepts, are the dominating approaches. Traction drives gain advantage from optimized power split transmissions, which consequently are being used in a growing number of applications. On the level of components, increase of efficiency and dynamics as well as power density are important trends. Altogether, design of systems and components is more and more based on modular concepts. In this sense, among others, sensors and control elements are being integrated to actuators; electric and hydraulic technology is being merged. In order to achieve maximum efficiency and performance of the entire machine, control of hydraulics has to include the whole drivetrain and the entire mobile machine in its application. In modern words, mobile hydraulic systems are a part of cyber physical systems.

In this research, the four valve independent metering configuration is to be investigated. The Independent metering concept will be emphasized and compared to spool valve coupled metering conventional technologies. Research focuses on the energy savings potential of the four valve independent metering configuration in addition to improving performance. The basic model of interest in this research is an actuator that is controlled by the four valve independent metering configuration to move beam like members of mobile hydraulic equipment such as tractor loader backhoes, excavators, and telehandlers. Five distinct (or discrete) metering modes that exist in the literature are initially studied: Powered Extension, High Side Regeneration Extension, Low Side Regeneration Extension, Powered Retraction, and Low Side Regeneration Retraction. The energy saving potential of these modes is studied and comparisons between this system and a conventional spool valve controlled actuator are conducted. The problem of switching between these five modes is treated as an optimal control problem of a switched dynamic system. Before solving the optimal control problem, a dynamic model for the system of interest is first derived. The model is experimentally validated. General theory for the optimal control problem is derived and then applied to the hydraulic system of interest. The results are then interpreted and explained by looking into the force-speed capability of modes. The effect of mode switching on system performance is studied as well. The basic mechanical system used for this analysis is a continuous rotating beam that undergoes structural vibrations due to mode switching in the driving hydraulic actuator. A fully coupled actuator-beam model is investigated. A non-dimensional analysis is pursued to generalize the study results. The optimal switching analysis and the vibrational study lead to the idea of Continuously Variable Modes (CVMs). Instead of having five distinct modes that determines the flow path by opening two of the four valves in the assembly, three Continuously Variable Modes are presented as an alternative way of controlling the four-valve configuration. These three CVMs combine the distinct modes and use three of the four valves to provide the fluid flow path. The five distinct modes become a special case of these three CVMs. It is going to be shown that CVMs have more force-speed capabilities than the distinct modes and provide for better velocity and vibrational performance by virtue of always offering a continuous flow path. The theory behind CVMs is presented and experimental validation follows.

Hydraulic systems represent a crucial part of the drivetrain of mobile machines. The most important drivers of current developments, increasing energy efficiency and productivity, are leading to certain trends in technology. On a subsystem level, working hydraulics are utilizing effects by improving control functions and by maximum usage of energy recovery potential. Independent metering and displacement control, partly in combination with hybrid concepts, are the dominating approaches. Traction drives gain advantage from optimized power split transmissions, which consequently are being used in a growing number of applications. On the level of components, increase of efficiency and dynamics as well as power density are important trends. Altogether, design of systems and components is more and more based on modular concepts. In this sense, among others, sensors and control elements are being integrated to actuators; electric and hydraulic technology is being merged. In order to achieve maximum efficiency and performance of the entire machine, control of hydraulics has to include the whole drivetrain and the entire mobile machine in its application. In modern words, mobile hydraulic systems are a part of cyber physical systems.

Independent metering valve systems open up for more flexibility because of the ability to control meter in and meter out flow individually, thus enabling many possibilities to adapt the actuator s behaviour to the user´s needs without altering any hardware. Furthermore, with alternative flow modes significant energy savings are possible. In many applications like excavators smooth switching between flow modes is required, a demand the market does not provide a satisfying solution for yet. Here, an approach using a short circuit path for smooth switching has been developed. The control algorithm hands over the volume flow from one path to another continuously depending on the current actuator load. Due to the flexible software structure the developed control algorithm can be applied to a very broad variety of independent metering valve layouts. Simulation results are promising and currently the solution is undergoing test rig evaluation.