PhD, University of Cincinnati, 2018, Engineering and Applied Science: Mechanical Engineering

Hypoid and spiral bevel gears are used to transmit power at a right-angle. They are generally used in automobiles, trucks, and earthmovers. This right-angle power transmission system is often plagued with severe noise and vibration problems. The source of this noise is due to the transmission error, which depends on the surface roughness of the meshing gear teeth, tooth profile errors, tooth deformations under the operating conditions, and misalignments. The surface roughness of the gear teeth affects the lubricant pressure. So, it is important to study the contact phenomenon that occurs in the meshing teeth to gain a better understanding of the powertrain gear noise problems. Thus, it is useful to study both the dynamics and the tribological parameters together. Tribodynamics refers to the study of effect of tribology on the dynamics of the contacting surfaces. Thus, the primary objective of this work is to develop a tribodynamic model for right-angled gear dynamics. This would enable a driveline analyst to study the combined effect of tribology and dynamics of the gears. This work aims to build a numerical model of the elastohydrodynamic lubrication in hypoid and spiral bevel gears. Therefore, a friction model is developed based on the full elastohydrodynamic lubrication and parametric studies are performed. The right-angle geared system is subjected to both rolling and sliding motions. Hence the study of contact parameters was performed based on the sliding and rolling motions that occurs at that position of the contact. This information is useful to the engineers to design the gear contact patterns in hypoid and spiral bevel gears. There are several dynamic parameters which can be synthesized from the elastohydrodynamic lubrication. In this work the damping and coefficient of friction are synthesized from the elastohydrodynamic lubrication. The time varying damping can be calculated from the elastohydrodynamic lubrication, which is more reasonable than usin (open full item for complete abstract)

Committee: Jay Kim Ph.D. (Committee Chair); Manish Kumar Ph.D. (Committee Member); Teik Lim Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2011, Mechanical Engineering

The tooth bending strength characteristics of spiral bevel and hypoid gears are investigated in this study both experimentally and theoretically, focusing specifically on the impact of gear alignment errors. On the experimental side, a new experimental set-up is developed for operating a hypoid gear pair under typical load conditions in the presence of tightly-controlled magnitudes of gear misalignments. The test set-up allows application of all four types of misalignments, namely the shaft offset error (V), the horizontal pinion position error (H), the horizontal gear position error (G) and the shaft angle error (γ). An example face-hobbed hypoid gear pair from an automotive axle unit is instrumented with a set of strain gauges mounted at various root locations of multiple teeth and incorporated with digital signal acquisition and analysis system for collection and analysis of strain signals simultaneously. A number of tests covering typical ranges of misalignments and input torque under both drive and coast conditions are performed to quantify the influence of misalignments on the root stress distributions along the face width. On the theoretical side, the computational model developed in earlier by Kolivand and Kahraman [31] is expanded to generate the root surfaces of spiral bevel and hypoid gears cut by using either face-milling or face-hobbing processes. A new formulation is proposed to define the gear blank and a numerically efficient cutting simulation methodology is developed to compute the root surfaces from the machine settings, the cutter geometry and the basic design parameters, including both Formate and Generate motions. The generated surfaces are used to define customized finite element models of N-tooth segments of the pinion and the gears via an automated mesh generator. Toot contact loads predicted by a previous load distribution model of Ref. [31] is converted to nodal forces based on the same shape function used to interpolate for nodal displa (open full item for complete abstract)

Committee: Ahmet Kahraman PhD (Advisor); Gary Kinzel PhD (Committee Member); Dennis Guenther PhD (Committee Member); Anthony Luscher PhD (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2020, Mechanical Engineering

In this study, computationally robust routines for hypoid surface generation and instantaneous contact line determination are proposed. The developed surface generation routine accurately defines undercut gear profiles for Face-Hobbed and Faced-Milled hypoid gears produced by Formate and generate processes. An approximation routine is incorporated into the developed surface generation model to obtain a stable initial guess for the non-linear solver. The proposed model successfully overcomes the computational challenges posed by higher order motion and complex blade profiles in the surface generation process. The efficacy of the developed routine was examined using industrial gear design having significant undercut, composite cutter profiles and generating motions. Unloaded Tooth Contact Analysis (UTCA) using the Ease-off method is outlined for obtaining the orientation and the location of the instantaneous contact lines. To enhance the accuracy for the prediction of the possible area of contact between gear and pinion, effects of roll angle on ease-off blank definition are investigated. A new blank definition routine for the Ease-off method is subsequently developed for accurate loaded contact analysis for the hypoid gears. The stabilization modules developed for the surface generation are extended to the Ease-off routines enhancing the robustness of the routines and enabling the visualization the complex cutter profiles (Toprem, Flankrem) and higher order motions.

Committee: David Talbot Dr. (Advisor) Subjects: Mechanical Engineering

PhD, University of Cincinnati, 2017, Engineering and Applied Science: Mechanical Engineering

Hypoid and bevel gears are widely used in the rear axle systems for transmitting torque at right angle. They are often subjected to harmful dynamic responses which cause gear whine noise and structural fatigue problems. In the past, researchers have focused on gear noise reduction through reducing the transmission error, which is considered as the primary excitation of the geared system. Effort on the dynamic modeling of the gear-shaft-bearing-housing system is still limited. Also, the noise generation mechanism through the vibration propagation in the geared system is not quite clear. Therefore, the primary goal of this thesis is to develop a system-level model to evaluate the vibratory and acoustic response of hypoid and bevel geared systems, with an emphasis on the application of practical vehicle powertrain system. The proposed modeling approach can be employed to assist engineers in quiet driveline system design and gear whine troubleshooting. Firstly, a series of comparative studies on hypoid geared rotor system dynamics applying different mesh formulations are performed. The purpose is to compare various hypoid gear mesh models based on pitch-cone method, unloaded and loaded tooth contact analysis. Consequently, some guidelines are given for choosing the most suitable mesh representation. Secondly, an integrated approach is proposed for the vibro-acoustic analysis of axle systems with right-angle geared drive. The approach consists of tooth contact analysis, lumped parameter gear dynamic model, finite element model and boundary element model. Then, a calculation method for tapered roller bearing stiffness matrix is introduced, which is based on the Finite Element/Contact Mechanics model of axle system with right-angle geared system. The effect of rigid bearing support and flexible bearing support is studied by comparing the flexible axle system model with rigid supported gear pair model. Other important system dynamic factors are also investigated, such as (open full item for complete abstract)

Committee: Teik Lim Ph.D. (Committee Chair); Michael Alexander-Ramos Ph.D. (Committee Member); Jay Kim Ph.D. (Committee Member); Manish Kumar Ph.D. (Committee Member) Subjects: Mechanical Engineering; Mechanics

Master of Science, The Ohio State University, 2016, Mechanical Engineering

Performance of a hypoid gear pair is critically affected by deviations of its gears from their desired nominal positions, also called misalignments. Such misalignments are known to move the contact patterns along the tooth surfaces, in the process changing loaded tooth contact stresses, root stresses and the motion transmission error of the gear pair. This experimental study focuses on quantifying the impact of misalignments on backlash, contact patterns, root stresses (durability metric) and motion transmission error (noise excitation) of a hypoid gear pair from an automotive rear axle unit. An existing hypoid gear test set-up that allows application of various misalignments is adapted. An encoder-based system is devised to measure motion transmission error. In addition, both of the test gears are instrumented with sets of root strain gauges. A test matrix that includes various misalignment configurations formed by pinion position errors, ring gear position errors, pinion offset errors and shaft angle errors is executed within a realistic range of operating torque. Impact of these misalignments on overall backlash, unloaded contact patterns, loaded transmission error, and pinion and ring gear root stresses is quantified. Results indicate that both transmission error and root stress amplitudes are significantly affected by the applied misalignments, indicating their direct influence on noise and durability performance.

Committee: Ahmet Kahraman (Advisor); Jason Dreyer (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2012, Mechanical Engineering

In this study, a computational methodology is proposed for prediction of power losses due to pocketing (pumping or squeezing)of oil at the mesh interfaces of spiral bevel and hypoid gears. The model employs an existing manufacturing cutting simulation procedure to define surface geometries of spiral bevel and hypoid gears cut through face-milling or face-hobbing processes. With the tooth surfaces defined, a novel hypoidal discretization method is proposed to define pockets of volume between the gear teeth in mesh along the face width and circumferential directions. With the volumes of each discrete pocket along with the exit areas and associated centroids as inputs, an existing fluid mechanics formulation that utilizes principles of conservation of mass, conservation of momentum and conservation of energy is used to compute load-independent power losses due to fluid pocketing. In the end, results of various simulations representative of typical automotive and aerospace conditions are presented to quantify pocketing losses within the operating speed and parameter ranges.

Committee: Ahmet Kahraman PhD (Advisor); Brian Harper PhD (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2010, Mechanical Engineering

An experimental investigation was performed in this study to quantify the influence of gear position errors and misalignments on the loaded static transmission error of a hypoid gear pair. A test machine was designed and procured for this purpose to allow operation of a hypoid gear pair under a given constant torque and at a very low rotational speed. The test set-up incorporated a capability to induce any type of misalignment at any user defined magnitude, including pinion (H), gear (G), shaft off-set (V) and shaft angle (γ) errors, independent of each other in a tightly controlled manner. An encoder-based transmission error measurement system incorporated with the test machine consisted of two high-precision angular optical encoders and a special-purpose analyzer to obtain the transmission error in both time and frequency domains. The test matrix considered in this study included all four types of misalignments at various magnitudes, drive and coast side conditions as well as a typical range of input torque. A 4.1 ratio hypoid gear pair from an automotive axle application was used as the example system. The test results were presented in the form of the variation of the first three harmonic amplitudes of the transmission error as a function of torque and error magnitudes. It was shown the each misalignment impacts the transmission error in different levels. The drive and coast side transmission error measurements were shown to differ as well. A nearly “V-shaped” dependence of the first harmonic amplitude of the transmission error to the torque transmitted was also documented regardless of the error type and magnitude applied to the gear pair.

Committee: Dr. Ahmet Kahraman PhD (Advisor); Dr. Sandeep Vijayakar PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2009, Mechanical Engineering

A computationally efficient load distribution model is proposed for both face-milled and face-hobbed hypoid gears produced by Formate and generate processes. Tooth surfaces are defined directly from the cutter parameters and machine settings. A novel methodology based on the ease-off topography is used to determine the unloaded contact patterns. The proposed ease-off methodology finds the instantaneous contact curves through a surface of roll angles, allowing an accurate unloaded tooth contact analysis in a robust and accurate manner. Rayleigh-Ritz based shell models of teeth of the gear and pinion are developed to define the tooth compliances due to bending and shear effects efficiently in a semi-analytical manner. Base rotation and contact deformation effects are also included in the compliance formulations. With this, loaded contact patterns and transmission error of both face-milled and face-hobbed spiral bevel and hypoid gears are computed by enforcing the compatibility and equilibrium conditions of the gear mesh. The proposed model requires significantly less computational effort than finite elements (FE) based models, making its use possible for extensive parameter sensitivity and design optimization studies. Comparisons to the predictions of a FE hypoid gear contact model are also provided to demonstrate the accuracy of the model under various load and misalignment conditions. The proposed ease-off formulation is generalized next to include various types of tooth surface deviations in the tooth contact analysis. These deviations are grouped in two categories. The proposed ease-off based method is shown to be capable of modeling both global deviations due to common manufacturing errors and heat treat distortions and local deviations due to surface wear. The proposed loaded contact model is combined at the end with a friction model based on a mixed elastohydrodynamic lubrication model to predict the load dependent (mechanical) power losses and efficiency of th (open full item for complete abstract)

Committee: Ahmet Kahraman Prof. (Advisor); Donald R. Houser Prof. (Committee Member); Gary L. Kinzel Prof. (Committee Member); Henry H. Busby Prof. (Committee Member) Subjects: Design; Engineering; Mechanical Engineering; Mechanics