Increasing the efficiency of the contact valve plate/cylinder block in axial piston machines

  Exploded View of an Axial Piston Machine

This research project focuses on the performance increase of the triboligical contact valve plate/cylinder block in axial piston machines, which are the most widely used type of displacement machines in hydraulics due to their robustness and high efficiency. The three essential tribological contacts are piston/slipper, piston/bushing and valve plate/cylinder block. State of the art in the contact valve plate/cylinder block is a hard/soft pairing to enable higher manufacturing tolerances and in addition, to avoid wear in case of solid body friction. A previous research project at ifas shows that the cylinder block is tilting nearly constantly towards the high pressure side. In the area of the minimum gap height, due to this tilting, the danger of solid body friction and temperature hot-spots increases. New concepts against the constant tilting of the cylinder block have to be developed which allow new coatings without toxic lead for a hard/soft pairing on the one hand and to enable a hard/hard pairing on the other hand. To reach this goal, the simulation model of the previous research project at ifas is optimized and used for the concept development. Prototypes will be designed out of these concepts for their experimental validation.

 
Benefit Procedure

Increased life and efficiency of the contact

Development of new concepts to avoid tilting of the cylinder block

New coatings without lead (hard/soft)

Derivation of the contact requirements for the concepts

New contact pairings (hard/hard)

Experimental validation of the simulation results

Testing of new contact pairings

Contact

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Local Extreme Load due to Tilting of the Cylinder Block

Schematic Representation of the Simulation Model

This project builds on the results of the project "Simulative und experimentelle Untersuchung des Kontaktes Kolbentrommel-Steuerspiegel in Axialkolbenmaschinen". Within the context of this project a simulation model was built, which is used and extended in the current project. The simulation model with its current status and the planned extensions in the current project is shown schematically in Figure 1.

 
  Simulation and measurement results for the minimum gap height in contact Piston drum and control mirror

With this simulation model, it is possible to investigate the processes in the contact betweem piston drum and control mirror for different geometries and parameters with low computing times of a few minutes. It could be proven that the piston drum tilts within a few revolutions. The minimum gap height is within a narrow angular range for both 4 and 5 pistons controlled in high pressure. The test bench trials confirm the results of the simulation. Figure 2 shows the results from the simulation and the experiment.

This locally almost constant minimum gap height leads to an extreme load on the surfaces in this area. On the one hand, the small gap height leads to solid contact and thus directly to abrasive wear. Furthermore, the solid body friction together with the increased fluid friction in this area lead to a strong temperature increase. In the worst case, this leads to destruction of the coating and thus to failure of the entire system.

 
 

Concepts to avoid tipping

In the research project presented here, various concepts are currently being developed to avoid tilting of the piston drum. The aim is to develop a system that does not impose a locally limited position of heat input on the tribological contact. The geometric adjustments in the contact have to be implemented into the simulation model and then investigated simulatively. With the help of the simulation results the concepts will be further optimized. This iterative process of simulating and evaluating a large number of different design variants is necessary for the targeted selection of suitable methods. First simulation results show the potential of some approaches.

 

Acknowledgement

The research project is funded by the German Research Foundation.

  Copyright: DFG