A novel fluid structure interaction and thermal model to predict the cylinder block / valve plate interface performance in swash plate type axial piston machines

The cylinder block / valve plate interface represents one of the most critical design element in the rotating kit of axial piston machines. The thin film of lubricant between cylinder block and valve plate has to fulfill simultaneously a bearing and a sealing function under dynamic load conditions; on the other hand, it represents an important source of power losses due to viscous friction and leakage flow. An accurate prediction of the time changing characteristics of the interface, in terms of fluid film thickness, dynamic pressure field, load carrying ability and energy dissipation is necessary to generate more efficient and reliable designs. However, the complexity of the physical phenomena involved in the interface\u27s operation made the trial end error practice the main design methodology in the last fifty years. The aim of this work is to deepen the understanding of the main physical phenomena affecting the cylinder block / valve plate interface performance. For this purpose, a unique fully coupled multi-body dynamics model has been proposed to capture the complex fluid-structure interaction phenomena affecting the non-isothermal fluid film conditions. The model is able of determining the fluid film thickness as a function of the interface\u27s load condition, accounting for the squeeze film effect due to the cylinder block\u27s micro-motion and the change in fluid film thickness due to the elastic deformations of the solid parts, caused by the fluid film pressure and by the thermal strains. In addition, the impact of micro-surface shaping introduced by design or resulting from wear process can be investigated and combined with the modification of the clearance due to the normal machine operation. The model was validated by comparing the predicted surface temperature of the valve plate with measurements for two different machines, a 100 cc and a 130 cc units of commercial production. In the first case the measurements were available in literature, in the second case an specific test stands was developed as part of the experimental study of the present work. The model has also been applied to the study of the impact of micro surface shaping on the performance of the cylinder block / valve plate interface