Power Drives and Controls

To decrease throttling losses in mobile hydraulic systems a number of new system architectures have been introduced in recent years. The concept of independent metering (IM), developed in the seventies, shows a lot of promise [1]. By allowing the meter-in as well as meter-out edges to be controlled separately, additional operating modes are created allowing a more efficient adaptation of system pressure to load pressure [2, 3]. Despite these advantages IM circuits have yet to find their way into industrial applications. This is mainly due to the related increase in component costs and more demanding control strategies. Additionally, the effect of mode switching on actuator motion and operator comfort is still unclear and considered to be a challenge. The STEAM mobile hydraulic system currently being developed in Aachen, Germany uses a number of new features to improve total machine efficiency [4]. Among others is the use of a new independent metering circuit called single edge meter-out control. Unlike other IM configurations, only one proportional valve is used to control cylinder motion. This paper introduces the new concept and discusses its advantages