A digital hydraulic multi-pressure actuator is a new actuator concept, which aims at lowering energy losses and decreasing dynamic requirements of a prime mover in mobile hydraulic applications. The actuator consists of an integrated hydraulic accumulator, which serves as an energy storage and a number of asymmetric cylinders acting as discrete pressure transformers. Leak-free on/off-valves are used to direct flow from the discrete pressure transformers to the actuator. Input power is supplied by charging the local accumulator with a small fixed displacement pump. Thus, the actuator requires only mean input power, while the output power peaks can be multifold. This paper concentrates on studying the controllability of the actuator concept and analyses the power losses and their sources through experimental study. The energy losses of the concept are measured in a mobile hydraulic boom mock-up and compared to earlier measured losses of a load sensing proportional valve based system. The measurements show that up to 77 % of the losses can be avoided by using the new concept. Three controller types are studied numerically and experimentally and their effect on control resolution and energy efficiency is evaluated.
Keywords: Digital hydraulics, Integrated actuator, Multi-pressure system