Date of Award

January 2015

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering

First Advisor

Andrea Vacca

Committee Member 1

Monika Ivantysynova

Committee Member 2

John Lumkes Jr

Committee Member 3

John M Starkey


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