SPUR GEAR DESIGN: SOME NEW PERSPECTIVES

Abstract

New perspectives such as harmonic mean, contact patch as translating third body, contact form factor, and service load factor are introduced in spur gear design. The harmonic mean rule characterizes the physical and geometric properties of the contact patch. The contact patch is construed as a body in translation during gear teeth engagement. The contact form factor may be used to compare the load capability of different pressure angle standards. The service load factor captures the influence of different conventional rated load modification factors. Gear design analysis is separated into design sizing and design verification tasks. Design sizing and design verification formulas are formulated and presented in simplified forms for the Hertz contact and the Lewis root bending stresses. Three design Examples are presented through which it is demonstrated that results from the contact and root bending stress capacity models compare very favorably with American Gear Manufacturers Association (AGMA) results. The worst differences in the results are 5.23% for contact stress in design Example 2 and-6.59% for root bending stress for design Example 1. In design Example 3, it is shown that using pinion teeth number higher than 17 or 18 can leads to overall size reduction of gearset. This is important because of possible manufacturing cost reduction and higher mesh efficiency. Comparison of proposed approximations for mesh overload, internal overload and service load factors for design sizing and design verification tasks yielded very close results. The highest variance in the three design examples between proposed approximated and AGMA values of these parameters is-5.32%, indicating a slightly higher or conservative value for design sizing. Due to the very favorable results in comparison with AGMA values, the design approach appears to be an acceptable one in the preliminary design of spur gears because of simplicity and transparency.