Efficiency of a variable displacement open circuit floating cup pump

The Floating Cup Displacement principle is a relatively new axial piston displacement principle for hydrostatic pumps, motors and transformers. Since its origin in 2001, it has been mainly applied in fixed displacement pump prototypes. At the SICFP’05, a design for a variable displacement open circuit Floating Cup Pump was presented. Now, the first prototype of a 28 cm3 unit based on this design, has been built. This papers reports the first efficiency measurements of this prototype. So far, the unit has been tested at 100% and 50% swash angle. The total efficiencies at these swash angles are already quite good, even if no design loops have been made yet. The paper further describes a new method to separate the losses in this unit over the different loss mechanisms. This method is used to distill the mechanical torque losses from the measurements. An inverse version of this method is then used to predict the total efficiencies of this unit at 25% and 75% swash angles.