A novel design concept for variable delivery flow external gear pumps and motors

摘要

This paper presents an original concept for variable delivery external spur gear machines, which combines the well-known advantages of these units (such as low cost, good reliability, acceptable efficiency) - traditionally fixed displacement - in a solution capable of varying the amount of flow displaced at each shaft revolution. The proposed design concept realizes a variable timing for the connections of each tooth space volume with the inlet and outlet ports, through a movable element ("slider") placed at the gears lateral side. The position of the slider determines the amount of flow displaced by the unit per revolution. In order to extend the range of flow variation achievable by the unit, an asymmetric involute tooth profile for the gears was proposed. A multi-objective genetic algorithm was used to optimize the design of the gears along with the design of the timing grooves in the slider. This algorithm is based on the HYGESIM (HY draulic GEar machines Simulator) tool developed by the authors' research group for the evaluation of the performance of every particular design. The optimal design solution, capable of achieving 40% flow variation (from 100% to 60%), was realized in a working proof of concept and tested for the case of a pump, although the solution is in principle valid for both pumps and motors. Experimental results were in line with the numerical predictions and show the potential of this design concept of achieving flow variations in an energy efficient fashion, with volumetric and hydro-mechanical efficiency at reduced displacements in line with other state of the art variable displacement units. Therefore, the proposed design can impact current applications for external gear pumps and motors, offering the additional flow-on-demand capability. Furthermore, it can be utilized in several other engineering applications in which traditional external gear machines were not a viable alternative because of their intrinsic fixed displacement nature.