Office for Technology Commercialization

Smaller, More Efficient Variable Displacement Pump

Technology #20160229

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Phase Shift PistonsPhase ShiftInline Piston Pump
James Van de Ven, PhD
Associate Professor, Mechanical Engineering
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Kim Stelson
Professor, Mechanical Engineering
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Eric J. Barth
Associate Professor, Mechanical Engineering, Vanderbilt University
Managed By
Kevin Nickels
Technology Licensing Officer 612-625-7289
Patent Protection

US Patent Pending US20180119689A1

Phase Shifted Piston Pairs

A novel alternating flow (AF) hydraulic pump combines the flow from pairs of oscillating pistons. By phase shifting the motion between the piston pairs, the combined flowrate of the pump is varied. This variable pump technology can be realized with a number of pump architectures include inline, axial piston, or radial piston. In the radial piston architecture, a common shaft drives two pumps with fluid lines connecting pairs of pistons between each pump. The first piston assembly is phase shifted from the second piston assembly so that pump displacement is varied using the phase shift between pump cases. The resulting variable pump assembly is highly efficient, axially short and power dense, and its design can be applied across a variety of hydraulics and displacement control applications.

Efficient, High-Bandwidth Displacement Control

Existing variable displacement hydraulic pump/motors are heavy, large, axially long (thus making common-shaft mounting challenging), and have poor efficiency at low volumetric displacements. While attempts to improve these pumps have increased the maximum efficiency, their efficiency is still poor at low volumetric displacements. As many applications require a pump to operate at low displacement for a large portion of the cycle, this results in significant energy loss. This new AC hydraulic pump technology enables efficient, high-bandwidth displacement control and allows compact mounting of multiple units on a common shaft for multi-actuator displacement control systems. The device can achieve effective variable displacement control in a significantly smaller and more efficient profile compared to existing designs.


  • Variable displacement pump system for dynamic control of multi-actuators with the pump displacement
  • Displacement control by merging multiple radial piston pumps on one shaft
  • Small axial profile allows for optimized space usage
  • Highly efficient compared to existing variable displacement pumps
  • High displacement density
  • Radial piston pump framework


  • Variety of hydraulics areas
  • Displacement control applications

Phase of Development - Prototype built and data collected.