Maha Fluid Power (Part 2) – Piston Micro-Surface Profile

Previously on iHydrostatics N10, we had an exciting tour in Maha Fluid Power center, I believe you have got the general overview of this top research center on the study of hydraulic efficiency. Reply N10 in Wechat iHydrostatics to read this post if you missed it. Any questions, comments or suggestions are warmly welcomed, iHydrostatics strongly encourages you to leave your comments in iHydrostatics QQ Group: 426372753.


In Part 2, iEditor will go to some details of the latest pump design idea. The frontier study of piston micro-surface profile impact on the piston pump efficiency will be introduced in this post. Normal design of piston is cylindrical, but how about sine-wave or barrel profile?

1Background
The lubricating gap between the piston and the cylinder must simultaneously fulfill both a bearing and a sealing function while also avoiding metal to metal contact along with minimizing dissipation due to leakage and viscous flow. The problem with reducing the losses though is that, as the lubricating gap becomes thinner, although the leakage is in turn reduced, the energy dissipation due to viscous friction will increase. Even more so, with a thin lubricating gap, metal to metal contact can occur causing wear or even failure.
The lubricating gap between the piston and the cylinder is also essential to the load carrying ability of the interface. External loads must be balanced by the pressure field generated in the fluid film in order to avoid critically low gap heights leading to mixed friction and wear. The pressure field is both hydrostatic and hydrodynamic.

Throughout the research both experimentally and numerically, it was understood that altering the shape and material of piston along with a balanced clearance could lead to a higher efficiency, a longer, more reliable life of the machine, and a larger load carrying capacity.

2New Piston Micro-Surface ShapeLubricating surface is the heart of piston pump, it mostly determines the life and performance. We all know that the piston design is always cylindrical, but what if the piston surface has other shapes? A lot of researches have been done to investigate the possibility and advantage of special shape design of piston surface. In this post, iEditor will show you what have been done in Maha Fluid Power Center on the study of special shape design of piston surface.

From 2008, Maha center had started working on the study of barrel and waved barrel like micro-surface shaping on the pistons surface as shown below. The research result demonstrated a reduction in energy dissipation along with friction work for the piston cylinder interface.

Also, in 2009 a wave like micro-surface shape was introduced on the piston’s surface (Filed patent: 61/165, 661)

3Effect of Piston Micro-Surface ShapeIn order to compare the positive effect of piston micro-surface shape, simulations have been done to investigate the advantages of various surface shapes. Sine wave surface, flat surface, barrel surface and waved barrel surface have been compared together.

Based on the novel fully coupled, thermo-elastic-hydrodynamic fluid structure interaction simulation model developed by Maha Center, the simulation results confirmed that by introducing a surface shape to the piston along with altering the configuration by decreasing the gap height between the piston and the cylinder, the energy dissipation was decreased and the load carrying capacity was increased over a wide range of operating conditions, especially at higher pressures, for both full and partial displacements.

Although this new technology is still in the lab phase without product application, as the developing of hydraulics, iEditor hopes the product with this new design won’t let us wait too long.

REFERENCES
[1]. Maha Fluid Power Research Center. 2014 Annual Report.
[2]. Ashley M. Wondergem. THE IMPACT OF THE SURFACE SHAPE OF THE PISTON ON POWER LOSSES. 8th FPNI Ph.D Symposium.

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