The Hydraulic Buck Converter - Concept and Experimental Results
Sprache des Titels:
6th International Fluid Power Conference Dresden - "Fluid Power in Motion"
The idea of so called hydraulic transformers, i.e. of devices that can rise or lower a
hydraulic pressure without much energetic losses, is by no means new. To a large
extent, the proposed technical realizations of this hydraulic principle have been
based on combinations of adjustable pumps and motors (see, e.g., /1/). Also
Achten’s celebrated hydro transformer /2/ belongs to this category of transformer
concepts based on variable displacement machines.
Other, physically different approaches for realizing a hydraulic transformer are
hydraulic switching converters which adopt analog concepts from electrical
engineering. To have an energetic advantage over resistance control such switching
converters must employ some inertia (or inductivity) effects. The simplest realization
of such a converter stems from Gall and Senn /3/. Their concept is based on the load
inertia and is rather limited in its performance if both, smoothness of the generated
motion and efficiency are relevant. In /4/ a converter concept is presented which
exploits the inertia of a hydraulic machine. Switching converter concepts based on
hydraulic inductivities have been discussed in /5, 6, 7/.
The hydraulic Buck converter is the simplest hydraulic switching converter and is
nearly a one to one transfer of the electrical Buck converter to hydraulics. Some
specific aspects of this converter, namely the modeling of wave propagation
phenomena in the pipe, the control of linear drives with this converter, and the
cavitation at the entrance to the pipe and means to avoid cavitation, have been
studied in /8,9,10/. But so far, no description of its basic properties by simple
mathematical models has been given. This and basic experimental results which
prove the feasibility of this hydraulic converter are addressed in this paper.