COMPREHENSIVE ANALYSIS, DESIGN, AND FABRICATION OF PERICYCLIC MECHANICAL TRANSMISSION WITH STRAIGHT BEVEL GEARS
Open Access
- Author:
- Mathur, Tanmay Dutt
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 26, 2019
- Committee Members:
- Edward C. Smith, Dissertation Advisor/Co-Advisor
Edward C. Smith, Committee Chair/Co-Chair
Liming Chang, Committee Member
Robert C. Bill, Committee Member
Francesco Costanzo, Outside Member
Christopher Rahn, Committee Member - Keywords:
- LTCA
EHL
Internal bevel gear
Pericyclic drive
FSM - Abstract:
- The Pericyclic drive is a breakthrough power-transmission concept that has the potential to address many of the problems posed by large gearboxes- noise, maintenance cost, and low power density. The key innovations of the Pericyclic drive are its nutational motion kinematics which enables dramatically enhanced gear ratios from a single gear stage (50:1), load sharing over many teeth (10% of tooth complement), and power density capabilities well beyond the current state-of-the-art. Kinematically, a Pericyclic drive is similar to Epicyclic gear trains with axes intersecting at large angles (175° - 178°). Traditionally, the usage of the transmission concepts that offer high reduction ratio in a compact space has been limited to very low torque applications. An extensive amount of work done has been in the field of Pericyclic drivetrains in the past decade to scale up the concept for large input power levels. Power flow in the mechanism and loads transferred to the components of the drivetrain - gears, bearings, and shaft are well understood. Baseline designs for Rotorcraft applications also exist. There have been ample concept demonstrations with prototypes, fabricated using additive manufacturing techniques, which operate under very lightly loaded conditions. There is however, a need to develop a comprehensive methodology that offers a detailed analysis of gear teeth contact when the drivetrain is loaded, a better understanding of component life and system efficiency, and a framework to select optimal design for any input conditions. This research attains three of the goals in the development of Pericyclic transmission technology: (i) mature the component level design analysis tools, (ii) integrate these individual design modules in a system level framework to design the transmission for given operating parameters, and (iii) use this framework to design a prototype for actual fabrication and testing under load. With the recent advances made by Gleason Inc. in internal bevel gear teeth cutting, it has become possible to fabricate a Pericyclic drivetrain that can take up large torque loads. Therefore, this work focuses on development of Pericyclic transmission utilizing straight bevel gear meshes. A detailed 3-D analysis of kinematics and dynamics of the Pericyclic drive mechanism is presented to realize the component level and gyroscopic loads in the system. A novel numerical loaded tooth contact analysis (LTCA) model is developed for the internal-external straight bevel gear mesh that exhibits large number of teeth in contact, well beyond the involute line of action limits. Due to high conformity of meshing gear surfaces, a parabolic profile modification is applied to the external bevel gear surface to localize the contact. A thick plate finite strip method (FSM) has been utilized to formulate the gear bending deflection. Based on the tooth deformation calculation model, a variational framework is developed to simultaneously solve for load distribution and gear tooth deformation field. This is followed by calculation of contact stress, bending stress, mesh stiffness, and transmission error. The solution is validated against FEA analysis carried out in ABAQUS. Thereafter, an elastohydrodyamic lubrication (EHL) model is developed to calculate mesh efficiency and Flash temperature rise. The effects of torque loads and gear micro-geometry parameters on all of the above mesh characteristics are also studied. A systematic methodology is developed to select appropriate bearings for the drivetrain, from existing catalogs. This is based on bearing fatigue life, efficiency, and weight considerations. The effects of inertial loads due to nutational motion of the internal bevel gear members are significant for bearing life calculations. Bearings have been shown to be the most critical components in the Pericyclic drive-system. The system level design procedure integrates LTCA, EHL analysis, bearing analysis, and shaft design, within a framework in which design decisions are guided by constraints posed by several factors such as assembly, ease of manufacturing, operational space, component life requirements, optimal component geometry and positioning etc. The designs for different input power levels obtained from the framework demonstrate the high torque per weight capability, and efficiency comparable to conventional multi-stage planetary drivetrains. Finally, a small scale 50 HP prototype design with a reduction ratio of 32:1 has been refined for fabrication and subsequent testing at NASA Glenn transmission test facility. The performance evaluation charts for the test article have been obtained from the overall system analysis model for validation against future test results.