With the wide use of axial piston machines of the swashplate type in industry, it is essential to maximize the overall efficiency of the machines. Focusing on the piston-cylinder interface, as it performs as a hydrodynamic bearing simultaneously fulfilling a sealing function, the overall machine can be improved by reducing the power losses due to viscous friction and leakage flow of this interface. This paper presents a research study in regards to altering the geometry of the piston through micro-surface shaping influencing the generation of the fluid film between the piston and the cylinder. This investigation utilizes a novel fully coupled fluid structure interaction model considering both thermal and elastic deformations of the solid bodies to predict the phenomena occurring within the fluid gap. Encompassed in this simulation study is a diversity of piston micro-surface shapes and a wide range of machine operating conditions. The designs presented include an axial sine wave, a flat, cylindrical design with tapered ends, a barreled shape, a combination of the axial sine wave and barrel, along with a circumferential sine wave. High pressure operating conditions in pumping mode as well as common operating conditions in both pumping and motoring mode are considered for the various designs. The results demonstrate up to a 30% reduction in energy dissipation from a standard piston-cylinder interface at higher pressure operating conditions (over 15% reduction considering all three interfaces of the machine) with the addition of a barrel surface shape while a 25% reduction (over 5% overall) is achievable at lower operating pressures in pumping mode with a waved barrel surface profile. As for motoring mode a 30% reduction (around 10% overall) is possible with the introduction of a waved barrel surface profile on the piston. It will also be shown, that not only are these reductions possible though microsurface shaping of the piston, but the reliability of the machine is also improved by reducing run-in wear all while maintaining a cost-effective, manufacturable design.

Axial piston machines are widely used in industry thus new cost-effective and highly efficient designs are needed. One way to increase efficiency and decrease cost is by altering the geometry along with the configuration of the piston/cylinder interface influencing the fluid film generation and in turn the energy dissipation and load carrying capacity while still having a design that is cost effective and easy to manufacture. This paper presents a study on a reduction of energy dissipation between the piston and cylinder over a wide range of operating conditions at both full and partial displacements based on the surface shape of the piston along with the minimum clearance. First, it is necessary to measure a base design and then compare those results to simulations in order to verify the simulation results. Once a baseline is established, various piston surface shapes and minimum clearances are then also simulated and compared back to the simulated baseline. Not only is energy dissipation important to compare, but also the minimum gap height over one revolution. The minimum gap height is in direct correlation to friction loss and wear. Therefore, this paper also includes an understanding of how the gap height affects the total losses thus leading to the importance of finding a relative clearance that satisfies a median between torque losses and leakage along with the importance of reducing the occurrence of critical gap heights to reduce the need for wear in in the machine.