New Model Enables Novel Piston Designs to Sharply Reduce Power Loss

Achievement date: 
2014
Outcome/accomplishment: 

Researchers at the Center for Compact and Efficient Fluid Power (CCEFP), an NSF-funded Engineering Research Center (ERC) headquartered at the University of Minnesota, have  combined experimental research with multi-domain modeling to develop an understanding  of the physics in thin fluid-film interfaces of pumps and motors. This understanding allowed creation of a state-of-the-art numerical model, which now enables generation of new designs aimed at reducing power losses in hydraulic systems.

Impact/benefits: 

Simulations using this model have demonstrated potential overall power-loss improvements ranging from 20% to 65% at varying pressures. These results represent a major breakthrough in this research direction and suggest an even deeper study of the possible new technology that will lead to a new generation of pumps and motors.

Explanation/Background: 

Swash-plate axial piston pumps and motors are widely used in today’s hydraulic systems. Thin fluid films separate highly loaded movable pump and motor surfaces from each other to prevent wear and machine failures. Although these lubricating films are essential, they also represent the largest source of power loss inside the hydraulic units. Despite many decades of worldwide intensive research, experts and pump designers still lack a complete understanding of the complex and physical behavior of these thin critical fluid films.

The model developed by the CCEFP researchers provides a tool to understand the physics in those thin fluid-film interfaces. This understanding of the lubricating-film physics enables generation of new design methods to reduce the power loss coming from gaps. The model provides accurate predictions (related to a combination of various micro-surface shapes and a decrease in the clearance between the piston and cylinder) and is being used to investigate the impact of micro-surface shaping on the piston surface, along with varying gap heights, on the overall performance of the machine (see figure). At higher pressures, simulations have demonstrated potential improvements of overall power loss up to 50% at full displacement and 65% at partial displacement; at lower pressures, improvements of up to 20% and 60% have been demonstrated.