This paper deals with a novel independent metering valve system which is intended to be used in medium sized mobile machines. The system uses a mechanical pressure compensator to enable a very simple SISO control algorithm which does not need any feedback parameters to be adjusted. The algorithm is capable of handling resistive and pulling loads at a certain desired velocity and inlet chamber pressure level. The paper gives a brief summary of the systematic approach to deriving the valves structure and compares different control approaches for the complete hydraulic system comprising several actuators. Special emphasis is given to the preferred solution, which is verified on a laboratory test rig consisting of reasonably priced mobile machine components. Furthermore a linear model of system and control structure is constructed to give detailed information regarding the dynamic characteristics of the controlled drive. The energetic benefits of the novel system architecture in comparison to a standard coupled metering flow sharing system are investigated by means of a levelling movement performed on the test rig and a simulated synthetic high power digging cycle.
Systems with independent metering offer a high potential for increasing the functionality and efficiency of valve-controlled hydraulic drives. But nowadays there are only a few prototypical applications. One reason for that are the so far insufficient safety investigations. Besides the structural investigations carried out at the research institute, this contribution deals with a fault detection by means of limit checking of the applied pressure sensors. A detection algorithm is derived from several software-in-the-loop simulations of the independent metering system applied at an excavator arm. The functionality and limits of the fault detection will be shown by means of measurements. As a result, all safety-critical faults can be detected which leads to a Diagnostic Coverage of DC = 99% and thus allows the use of independent metering up to a Performance Level PL = e.
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