Adaption hydraulischer Verdrängereinheiten an umweltverträgliche Basissysteme

Research Engineer Dipl.-Ing. Claus Enekes
Room 222, Tel. 0241/802-7524

 
Context

Hydrostatic pumps and engines are essential components of hydraulic mechanisms. They transform mechanical energy into hydraulic energy and vice versa. Hydrostatic machines and their standard fluids based on mineral oils have developed to a high technical standard. In order to withstand the operating loads, engineers have made considerable effort to find the best combination of additives. The fluids in this case are not biologically harmless and often toxic. In case of the future use of enviromentally friendly fluids without additives the important trobological qualities of the fluid must be found in the materials instead. This can be achieved by the new designed PVD-coatings.

Analysis

Considerations of displacement units show the most stressed tribological systems. These systems are (picture 1):

  • cylinder / valve plate
  • guide shoe / swash plate
  • plunger / cylinder bore
  • ball joint / guide shoe


picture 1: tribological systems

The tests of tribological systems by applying coatings to the existing components are expensive and time-consuming. It is quite impossible to measure and regulate the appearing stresses. Therefore a simplified test (picture 2) is performed which makes a preselection of the new coatings possible. Further test can be based on these experiences. In the tribometer statements about the friction, wear and surface can be ascertained.


picture 2: friction measurement instrument

First studies are based on fundamental principles by Siebel/Kehl (picture 3).


picture 3: test pieces

Tests (picture 4) have shown, that it is absolutly possible to improve the wear and friction properties by PVD-coatings.


picture 4: test schema

Coatings containing carbon have the possibilities to fulfil purpose of wear protection and decreasing friction. The coatings HfCg and ZrCg, that have been worked out in cooperation with Material Science Institute RWTH Aachen, show an excellent adaptability to the occuring stresses due to their graduated structure (picture 5).


picture 5: HfCg-Coating

A few results of the wear and friction studies are shown in the pictures 6 and 7.


picture 6: friction


picture 7: wear