An innovative working concept for variable delivery flow external gear machine

Ram Sudarsan Devendran, Purdue University

Abstract

An innovative and unique working concept for variable delivery external gear machines (VD-EGMs) is presented in this study. The proposed design not only encompasses all the well-known and important advantages of traditional external gear machines but also introduces a feature for varying the displacement (flow delivered per unit revolution). The novel principle of achieving variable displacement in EGMs is based on the variable timing of the connections of the displacement chambers/tooth space volumes (TSVs) with the inlet/outlet ports. The timing variation is obtained by the addition of a simple element (called a “slider”) within the lateral bushings. The position of the slider determines the amount of flow displaced per unit revolution. Starting from the geometry of the design and the proposed concept, analytical expressions for predicting displacement variation, flow rate and input shaft torque were derived. With this working principle, the range of variation of the displacement can be significantly increased by modifying the gear profiles. Therefore, in this work, novel gears with asymmetric teeth profile are designed with the help of a novel tool developed particularly for this process. However, due to the inherent nature of the displacing action of the EGM due to the meshing of the gears, it is not possible to achieve a full flow variation from 0%-100%. Therefore, to maximize the range of flow variation while considering all the other important performance features of the machine to be maintained at an optimum, a multi-objective genetic algorithm based optimization method is used to identify the optimal design of gears and grooves in the lateral bushings. The performance of the design configurations were analyzed in detail by using HYGESIM (HYdraulic GEar machines SIMulator) Simulation tool. An optimal design of the machine was identified which was capable of maximizing the reduction (100%–68%) in flow variation, thereby providing lower delivery flow at the expense of reduced torque (hence reduced input power). The validity of the proposed novel VD-EGM was demonstrated using a proof of concept test performed using the prototypes of the optimal design. The simulated results provided by HYGESim were validated with those obtained from the measured data thereby accomplishing a very good agreement between the experimental data and the model predictions. The successful proof of concept test results, lead to the design of two flow control actuation systems which represent a manual system and an automatic pressure compensated system. The performances of the prototypes were analyzed using a steady state test rig. Experimental results show that the flow rate and input shaft torque reduces proportionally with displacement in the case of the manual flow control system. The measured volumetric efficiencies at lower levels of displacement were found to be lesser than those at maximum displacement, which are in line with the performance of typical other VD units in the market. The flow control actuation system based on pressure compensator principle was designed to reduce the flow automatically depending on the pressure at the outlet. Experimental performance of the VD-EGM with pressure compensated actuation system show that the delivered flow reduces automatically after the preset pressure is reached. The input shaft torque was also seen to reduce proportionally with the corresponding displacement. The experimental results show positive potentials in the working concept of the VD-EGM, which would lead to a new direction in designing cost effective VD units that can be used in place of fixed displacement units to provide the additional flow on demand functionality; thereby significantly increasing the overall energy efficiency of the hydraulic system in which the VD-EGM is used.

Degree

Ph.D.

Advisors

Vacca, Purdue University.

Subject Area

Mechanical engineering

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