Fluid Power Research Update: Variable Displacement External Gear Machine

The Center for Compact and Efficient Fluid Power (CCEFP) is a network of researchers, educators, students and industry working together to transform fluid power—how it is researched, applied and taught.  CCEFP fluid power research is creating hydraulic and pneumatic technology that is compact, efficient, and effective.  We are pleased to share an update on the Variable Displacement External Gear Machine, led by Professor Andrea Vacca at Purdue University.

Variable Displacement External Gear Machine

Submitted by: Professor Andrea Vacca, Purdue University

This CCEFP-funded project aims at formulating and implementing an innovative approach for variable flow pumps. The proposed concept is based on the displacing principle typical of external gear machines (EGMs), and preserves the typical advantages of traditional fixed displacement EGMs, which are: low cost, good energy efficiencies, reliability and tolerance to fluid contamination. The main idea for achieving variable displacement is based on attaining a variable timing of the connections of the internal tooth space volumes with the inlet/outlet ports. This is achieved by controlling the position of the “slider,” an element introduced at the lateral side of the gears. The tooth profile of the gears was particularly conceived within the research, to permit a wide range of flow regulation. A prototype pump suitable for high pressure (up to 250 bar) applications was realized and tested at the Maha Fluid Power Research Center of Purdue University. Measured results show confirmed the possibility of regulating the flow (between 65% to 100% of maximum flow) with high efficiency. As additional features (relief function), the slider permits to further reduce the flow (up to the null flow condition) by throttling fluid from the outlet to the inlet. The proposed principle is particularly suitable for all applications that requires a partial flow regulation: from traditional fluid power applications (fan drives, charge pumps, etc.) to low pressure applications (fuel injection, washing systems, etc.).

The proposed concept permits the implementation of different actuation concepts to control the flow. In particular, the realized prototype (Figs. 1 and 2) permits to demonstrate two different flow regulation concepts: a manual flow regulation system and a pressure limiter. However, other systems such as a load-sense flow regulator or an electro-hydraulic flow regulator can be easily implemented.

Current research is directed towards the realization of a prototype capable of efficiently vary the flow in the 50%-100% range. Moreover, it is under study the realization of a prototype for low pressure applications that includes an electro-hydraulic system for the flow regulation.

Figure 1 Variable Displacement External Gear Machine

Figure 2 Exploded view of the prototype with pressure compensator (patent pending)

About Professor Vacca:

Dr. Andrea Vacca  earned his Master’s degree – with honors – in Mechanical Engineering from the University of Parma (Italy) and his doctorate in Energy Systems from the University of Florence (Italy) in 2005. For both degrees he presented theses in the field of Heat Transfer and Gas Turbine Blade Cooling Technology. Before joining Purdue University as Assistant Professor in 2010, Prof. Vacca was Assistant Professor of Fluid Machinery at the University of Parma (Italy).  Professor Vacca is the author of more than 80 papers, most of them published in international journals or conferences. He is also active in the fluid power research community. He is a faculty member of the Center for Compact and Efficient Fluid Power (CCEFP), and he is currently chair of the SAE Fluid Power division. Prof. Vacca is also Treasurer and Secretary of the Board of the Fluid Power Net International (FPNI). Furthermore, he is an Executive member of the Fluid Power Systems and Technology Division (FPST) of ASME. He is also Associate Editor of the International Journal of Fluid Power.

Contact: avacca@purdue.edu