Traditional valve controlled hydraulic drives have an inherent power loss, due to the throttling over the valves, which limits the maximum system efficiency. Pump controlled direct drives do not have this inherent limitation, but are limited when it comes to controlling asymmetric cylinders, why most solutions that have tried to overcome this problem have incorporated some kind of accumulator. In the present paper a new concept is presented, modelled and analyzed, and it is shown that the concept overcomes the problem with asymmetric cylinders, without the use of an accumulator. The paper first presents an analysis of the general concept, showing that both cavitation and excessive pressure build up needs to be handled by the system, after which the system is presented and modelled. Finally both simulation and experimental results are presented showing the validity of the concept.
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