Entwicklung eines Softsensors für hydraulische Schieberventile

RWTH Publications (RWTH Aachen)

Abstract

Hardware-based flow meters in hydraulic systems increase costs, add additional pressure losses, require integration effort, and may limit measurable dynamics. This thesis therefore investigates whether a proportional valve with digital on-board electronics can be used as a software-based flow-rate sensor and what accuracy can be achieved under application-relevant conditions. The sensing concept follows a three-stage dependency chain: (1) actuator axial force is estimated from coil voltage, coil current and spool position, (2) after decoupling disturbing effects, the hydraulic flow force acting on the spool is derived, and (3) a valve-specific map converts flow force and spool position into flow rate. Two key challenges are addressed. The first is strongly operating-point-dependent friction, which masks the flow force. To enable robust online flow-force estimation, an active dithering-based measurement and evaluation method is developed. It cyclically probes the friction band and provides a reproducible estimate through averaging. In addition, a significant influence of fluid temperature on flow forces is demonstrated and a compensation method is derived. The second challenge is real-time force estimation. For axial-force estimation, data-driven models are implemented and compared, in contrast to common practice. As a contribution to robust identification, a model-based optimized APRBS excitation with warm-start and a systematic evaluation of input–output space coverage is presented. Furthermore, a model-based position control and a con-trolled dither are realized; dither parameters are tuned via optimization. The soft sensor is validated on a test rig against a screw-type flow meter. Across the investigated operating points, mean error, standard deviation and mean absolute error remain predominantly below 1 l/min and reach a maximum of 2,6 l/min, corresponding to approx. 1,3% and 3,5% of full scale. Despite filtering, short transient error peaks of up to about 33 L/min occur synchronously with rapid position and pressure steps and are mainly caused by reference dynamics and synchronization limitations as well as pressure shocks. Therefore, performance assessment in these transients is only possible to a limited extent. Overall, the results show that a software-based sensor for flow-rate estimation can be realized with high accuracy under application-relevant conditions. Finally, the findings are condensed into a design methodology. In addition, an application is presented that enables a rough suitability and error assessment for further valves, supporting transfer to industrial practice.

Authors 1

1. Simon Hans Gerd Hermann Hucko corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen