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O+P Fluidtechnik 7-8/2018

O+P Fluidtechnik 7-8/2018


IFAS JUBILÄUM FORSCHUNG UND ENTWICKLUNG 07 08 Setup, methods and goal of SFB 442 Self-energizing hydraulic brake – SEHB 4 TH DECADE – THE 2000 TH One research highlight in this decade was the collaborative research center (Sonderforschungsbereich) SFB 442. Its goal was to research and develop environmentally friendly tribological systems for exemplary use in machine tools. The main idea consisted in transferring the additive functions of fluids to the material surfaces of the tribological partners. Therefore, biologically fast degradable and non-toxic fluids were developed by using slightly dosed and environmentally friendly additives. In order to take over the missing lubrication and wear protection features by the material compounds of the tribological bodies basic research work was done to determine suitable composite materials. The basic course of action adopted within SFB 442 is described in Fig. 6. The starting situation provides for the redesign of tribological systems on the basis of mineral oils and the aim was to achieve the effects of the surface-active additives by transferring the additive functions directly into the surfaces. This required research into and development of new ester fluids based on oleic acid methyl esters, as well as efficient coating systems, which are capable of performing the functions of the additives. Graded carbon coatings and coatings of hard material were worked out as a function of the respective tribological system and adapted to meet the specific requirements for the point or area of contact. A machine tool with both components and processes capable of running on environmentally compatible lubricants was utilized within the research project. At the same time, the concept had to allow for the methodical approach of integrating environmental protection into the production process in accordance with the EU regulatory framework for Registration, Evaluation and Authorization of Chemicals ( Having successfully completed all 4 phases within a 12+ year funding span, today it is possible to design tribological systems with the help of the design and dimensioning method that incorporates the knowledge acquired from those scientific results which are stored and accessible in a database. Many interdisciplinary dissertations resulted and just those from IFAS are listed in Fig. 7. Two professors that qualified within this research 42 O+P Fluidtechnik 7-8/2018

IFAS JUBILÄUM 09 Simulation of tribological contacts in axial piston pumps activity became Professors at RWTH Aachen University. It is Prof. Kirsten Bobzin (IOT) and Prof. Christian Brecher (WZL). The next example for this decade is the invention, research and development of the self-energizing hydraulic brake. It can be seen as the hydraulic pendant of the self-energizing mechanical wedge brake. The functional principle is displayed in Fig. 8. It is based on an invention and patent from Prof. Stammen and described in many publications and his habilitation thesis of 2009. The basic idea is to attach the brake body not directly to the chassis or bogie but to use a supporting cylinder in between. During braking it allows a pressure build up in the cylinder. This pressure is then used to supply the servovalve of the brake actuator. Main advantage is the closed loop brake control which is possible because the measured pressure in the supporting cylinder is directly proportional to the braking torque thus allowing braking torque control. Another advantage is the integrated power pack because the brake energy is directly used out of vastly available energy dissipated during braking. Having obtained the qualification for the use at DB ifas is now working on a technology transfer project financed by DFG to apply a controlled version for a tram. Prof. Stammen earned the prestigious NRW Wissenschaftspreis in 2007 for his invention. Lots of publications document related work and three dissertations listed in Fig. 8 document the intensity of research work on the subject. Another very active and challenging field of development deals with the tribological contacts in displacement machines. The principal cross sectional set up of a swash plate unit addressing all tribological contacts is displayed in Fig. 9. In fluid power the necessary gaps have two functions. The first is to seal chambers with moving walls by functional gaps and the second is minimizing friction on sliding surfaces. A lot of involved test stand design came up over the years of research into this subject at ifas. One example is shown in the upper right side of the figure addressing measurements of leackage and friction torque between piston drum and control plate. Another test stand addresses the piston moving in its bore under operating conditions. These tests being very involved and taking long preparation and operation time the research thrust concentrated on the development of simulation programs to obtain design results and optimization runs just by simulation. It is possible to use very sophisticated CFD and FEM tools for the simulation. However, this takes a lot of simulation time and doesn’t lead to quick results that the engineer needs. So the development task was to design simulation tools that deliver quick results within minutes rather than days. This set the birth of research work conducted by Stephan Gels and documented in his doctoral thesis published in 2011. He developed a simulation tool for the piston-bushing contact and was able to demonstrate its validity by comparing the results to measurements. He then showed that optimization runs are possible to optimize the gap contouring of piston and bushing. Later on, the methodology was also applied to the piston drum and control plate by Stephan Wegner whose dissertation will be published shortly. This research provides information on the methodology and shows examples for its simulation accuracy as well as the speed by which results are obtained. Demonstrations of the impressive features are illustrated by videos and are verified by tests with units available on the market. It extends well into the future and for readers interested, links to literature into the subject are available on our home page calling and searching by the names of the researcher. The upcoming issue will highlight the research of the current decade as well as the plans of the institute for the future. Prof. Dr.-Ing. Hubertus Murrenhoff, former Director of ifas, and Prof. Dr.-Ing. Katharina Schmitz, new Director of ifas since March 2018, Institute for Fluid Power Drives and Systems (ifas), RWTH Aachen University O+P Fluidtechnik 7-8/2018 43


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