A STUDY ON DESIGN SPACE APPROACH FOR DESIGNING AN OPTIMIZED HELICAL GEAR PAIR, FOR DIFFERENT GEAR MATERIALS

Abstract

The work presented in this dissertation:; deals with optimization of a helical gear set. Attention is focused upon reducing the volume of a gear set subjected to constraints on bending stress, pitting stress and involute interference of gear teeth. Before proceeding to the actual design and optimization aspect, a brief review iS done on the work of similar nature that was done by experimentalists and designers in the past. The review indicates that design of compact gear involves a complicated algebraic analysis. A series of iterations is normally required to arrive at a practical combination of pinion teeth and module. No simple straight forward method is available to solve such a complicated problem. In the view of the increasing demand for improving the helical gear design methodology and reducing the expensive time of designer it has now become essential for modern manufacturing units to implement advanced methodology to get a safe optimal helical gear. The present work presents a new approach to helical gear problem. The new method makes use of some newly defined dimensionless parameters. In the resulting design space, the optimal dimensionless design (which defines the optimal tooth geometry) is independent of load, and speed requirements of the gear set. However the optimum is dependent on the physical properties of materials used. A new parameters called material properties relationship factor, Cmp is introduced. In the problem formulation,, it is shown that optimum will always be constraint bound and it will occur at one of the three possible constraint intersectors. Cmp is used to identify which of three possible constraint intersection is correct one. The program generates the dimensionless design space by properly_ locating the bending, pitting and interference mode of failure curve segments, identifies the safety. zone and locates the correct optimal point. An attempt has been made to critically examine the mode of failure under different operating conditions. The effect of gear ratio, helix angle and material properties of twenty gear materials on the feasible optimal volume has also been studied. Tabulated optimal dimensionless designs are included for some standard sets of tooth proportions. An example which shows 'how to transform the solution back into real design space considering load and speed requirements of the gear set is also presented: