Nested Planetary Geartrain Design for Vibration Reduction Using Augmented Direct Gear Design Methodology
The Noise, Vibration and Harshness (NVH) of a vehicle is one of the decisive indices of vehicle performance in terms of objective measures and subjective quality. The compact co-axial planetary geartrain of the automatic transmission, with its advantages of high gear reduction, controllable power split, distributed torque on multiple gears, and the ability to shift under load, is an irreplaceable core component in a vehicle's powertrain. It plays an important role in providing a smooth, stable, and quiet ride. However, due to the complexity of planetary gearsets and various operating points of engine-transmission power matching, the planetary geartrain is also identified as one of the major contributors to noise and vibration. The vibration reduction of the planetary geartrain is essential for attenuating the vehicle's NVH. Over the past two decades, an increasing number and wide range of research topics have been conducted on the mechanism and prediction of the planetary gearset noise and vibration. Finite Element Analysis provides high fidelity tooth contact modeling analysis of a planetary gear set. The lumped parameters modeling was largely adopted to discover the dynamic behaviors of gearset such as vibration mode properties and forced responses. Planet load sharing and planet phasing have been investigated and proven to be greatly related to gear noise and vibration. The tooth profile modification exploration showed numerical evidence of the effectiveness of reducing the mesh forces so as to reduce the resonances in planetary gears. Other topics, relating to planetary gear noise and vibration such as component elasticity, high-speed effect, manufacturing error and experiment validations etc., were also widely discussed. A few studies were conducted on the dynamic issues of compound planetary geartrain, however, little attention was paid to the nested planetary geartrain. Despite its long history and wide usage, the planetary geartrain still experience noise and vibration issues which need to be explored and solved. Direct Gear Design is a new gear design method that finds its applications in various fields, such as aerospace, agriculture, automotive, robotics, etc. It focuses on customized tooth macro geometry optimization, symmetric and asymmetric teeth, gear performance maximization and gives a flexible approach to gear design. However, it does not involve the tooth micro-geometry such as tooth profile modification that greatly affects gear NVH. This dissertation augments the method by adding micro geometries to the profile expressions. A function on Line of Action is developed to describe the true profile which differentiates from the pure involute profile. The augmented method is used for gear mesh process analysis, meshing stiffness derivations and initial profile modification selection. Analyses for effect of micro geometries were conducted through Romax by evaluating Transmission Error (TE) and amplitude of teeth harmonics. The results show a great reduction on both the Peak to Peak Transmission Error (PPTE) and the teeth harmonic amplitude, thus the excitation to the geartrain can potentially be decreased. Design for Six Sigma (DFSS) method was adopted to determine the optimal combination of profile modifications that are suitable for multiple work conditions. Unfortunately, the effect of phasing on geartrain dynamics was not able to be performed due to the limitation of the software. An analytical model is necessary to address this factor as well as the body flexibility in the future.
Zhang, Purdue University.
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