Title

Tooth profile modifications for optimum dynamic load in spur gears based on pseudo-interference stiffness estimation method

Date of Completion

January 2005

Keywords

Engineering, Mechanical

Degree

Ph.D.

Abstract

A systematic methodology combining an optimization technique, three dimensional analytical rigid body dynamics and a novel method for non linear stiffness analysis, namely Pseudo-Interference Stiffness Estimation method (PISE), is proposed to aid engineers and gear designers to dramatically reduce gear design time and improve the existing spur gear system performance. One of the major concerns in gear design is the reduction of gear dynamic load. Minimizing gear dynamic load will decrease gear noise, increase efficiency, improve pitting fatigue life, and help prevent gear tooth fracture. Therefore, the proposed method is aimed at minimizing this force by utilizing tooth profile modification techniques, tooth crowning and shaving. The main aim of this methodology is to search for the optimum profiles of tooth crowning and shaving that eventually lead to the optimum dynamic tooth load in the gear mesh. Additionally, this method is easy to implement and computationally inexpensive. To validate the proposed method, a detailed design study is numerically investigated and compared with experimental data from NASA and other sources as reported in the literature. The results have shown that the dynamic tooth load can be reduced up to 50 percent of its original value. However, this reduction is only valid at the operating ranges of the design load and design speed When the optimized gear system is operated at of design speed and off-design torque, its dynamic load may change significantly. It is also found that the effect of profile modification on the dynamic response of the gear system was mostly observed to be a reduction in the peak dynamic tooth load at the resonance speed. ^ Later, the investigation of gear tooth durability was conducted to validate an improvement of gear life. The rating factors given in AGMA publication, Hertzian contact stress, bending fatigue stress, flash temperature and PV index are employed in gear durability determination. The values of these quantities along the line of action were evaluated and plotted to illustrate their distribution. The results show that, with the reduction of 50 percent in dynamic tooth load, the reductions in PV index, bending fatigue, Hertzian contact stress, and flash temperature can be achieved up to 64, 58, 28 and 39 percent, respectively. Thus, this guarantees that the risks of pitting failure, scoring failure and tooth fracture are greatly improved. Besides, the variation of these quantities along the line of action explicitly indicates that pitting failure is likely to occur around pitch point and points in tip and dedendum zones are prone to scoring failure. ^

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