Tooth Root Bending Strength of Gears: Dimensional Effect for Small Gears Having a Module below 5 mm

Franco Concli

doi:10.3390/app11052416

Abstract

Downsizing is a more and more widespread trend in many industrial sectors, and, among the others, the automotive industry is pushing the design of its components towards increasingly compact, lightweight, efficient, and reliable solutions. In the past, the drivetrains for automotive were designed and manufactured with gears having modules in the range 3 to 10. In this respect, the main actual European standards for gear design such as ISO 6336:2019 (based on the DIN 3990:1987) are validated in the 3 to 10 mm range only. Moreover, it is well known that, by increasing the gear size, the gear size factor for tooth bending YX reduces. However, nowadays the advances in terms of materials and design knowledge have made possible the realization of miniaturized gearboxes with gears having normal modules below 3 mm with comparable (or better) reliability. In this scenario, understanding how the size affects (positively) the load-carrying capacity for tooth root bending for small modules below 5 mm is fundamental to maximize the design effectiveness in case of downsizing of the drivetrains. In this paper an experimental study was performed on small gears made of 39NiCrMo3 having a normal module of 2 mm to verify the load-carrying capacity for tooth root bending. Based on the experimental evidences and additional data from literature and past studies by the author, an extended formula for the size factor YX (according to ISO 6336) is proposed.

Highlights

In the recent years, downsizing is emerging as a global trend
In order to evaluate theand influence ofFine-Module the gear sizeGears on the load-carrying capacity for Methods: tooth bending, Single Tooth Bending Fatigue (STBF) [27] tests were performed on a gear
Dobler et al proposed a new formulation for the size factor YX based on experiments performed on gear samples made of 16MnCr5 and having modules between 0.45 and 20 mm

Summary

Introduction

In the recent years, downsizing is emerging as a global trend. The miniaturization of the mechanical systems, at least in the automotive sector, is pushed by the more and more stringent environmental restrictions such as the EuroX standards; reducing the size and the weight of the drivetrain has a significant impact on the fuel consumptions and pollutant emissions [1,2]. Demonstrated that an increased gear size promotes a decrease in the load-carrying capacity for tooth root bending While this effect is well supported by evidence for modules over 5 mm [15,16,17,18], few data are available below that threshold [19]. Tion and the bending moment arm h relevant to load application at the ou The occurring stress σF (Equation (1)) results single pair gear tooth contact according to ISO 6336—Method B is shown in F. It is interesting to notice that, according to the model proposed by Dobler et al, based on several results available in the literature, for modules over 5 mm the load-carrying capacity for tooth root bending decreases.

Material

Method

Discussion

Proposal of a New Formulation for YX

Conclusions