Tip-root interference analysis and determination of load carrying capacity for high contact ratio spur gear pairs

Spur gear pairs with high contact ratio (HCR) are used in situations where the load carrying capacity is required to be higher than the gears with standard contact ratio (SCR). The tooth structures of HCR gears are longer and thinner than those of standard gears. This condition increases the risk of tip interference between the HCR gears during operation. For this reason, appropriate values must be selected by determining restrictions for parameters such as the tooth addendum coefficient, dedendum coefficient, operating center distance and pressure angle. Within the scope of this thesis study, spur gear pairs with SCR profile are converted to HCR profiles using various scenarios. For this process, a code is developed using Matlab software and geometric constraints such as tip-root interference and top land thickness are applied. The developed code is able to generate SCR and HCR gear pair profiles by giving the necessary inputs, determine all geometric alternatives for the conversion from SCR to HCR, and offer the most suitable HCR gear pair in terms of the load carrying capacity. AGMA-913-A98, AGMA-908-B89 and AGMA-2001-D04 standards are used as references throughout the design process of the gear profiles. The gear profiles converted from SCR to HCR are verified by comparing with the results of KissSoft software, which is widely used in the industry. In addition, by calculating the bottom pressure for the gear pairs converted from SCR to HCR, the optimum HCR gear pair that can carry the highest load among the alternatives is determined. In this way, it is observed that how much load advantage is achieved by converting from SCR to HCR. According to the results obtained, HCR gear pairs can provide up to around 32% elevated load carrying capacity compared to SCR gear pairs.