Master of Science, The Ohio State University, 2024, Mechanical Engineering

The design of transmission components must meet multiple performance requirements to ensure they are durable, efficient and quiet. In certain applications, weight reduction is an additional requirement especially for an aerospace system. Towards this goal, material is typically removed from the gear bodies, resulting in gear rims and webs that are rather flexible. Such flexible-rim gears might involve a class of dynamic behavior associated with the deformable-body vibratory modes. If the transmission is operated at resonances associated with these modes, it may result in adverse dynamic loading conditions. The main focus of this thesis is to develop an experimental means of quantifying such deformable-body behavior of high-speed gearing. A new test machine is developed to study the contributions of deformable-body modes of a flexible-rim spur gear to the overall dynamic behavior in a lab environment under realistic torque and speed conditions. Several measurements systems are designed and implemented to monitor key features of deformable-body motions such as accelerations, displacements and strains. Simple and repeatable methods of introducing manufacturing variations in the experimental set-up are developed in order to quantify the impact of such variations have on vibratory models of flexible-rim gears. The methodology is employed to establish a baseline (no-error) database and demonstrate the deviations from this baseline behavior due to manufacturing variations. These results indicate that the proposed methodology is effective in investigating flexible-rim behavior.

Committee: Ahmet Kahraman (Advisor); Isaac Hong (Committee Member); Carlos Castro (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2018, Mechanical Engineering

In this study, a two-dimensional model is proposed for determining theoretical contact lines, tooth separation, and approximated loaded transmission error with frequency spectra thereof, as well as various other output variables such as instantaneous center distance, operating pressure angle, and instantaneous contact ratio when circular runout error is applied to either or both gears in a spur or helical gear pair. As an addendum, a method for calculating off-line of action tooth separation using this model is described for spur gears. Additionally, a three-dimensional model is proposed for determining theoretical contact lines and tooth separation when any combination of circular runout or wobble error are applied to either or both gears in a spur or helical gear pair. Sample analyses are shown for spur and helical gear pairs with runout error applied using the two-dimensional model, and a helical gear pair with various combinations of runout and wobble error applied using the three-dimensional model. The results are discussed qualitatively with respect to the expected effects the applied errors would have on the tooth separation and related variables.

Committee: David Talbot (Advisor); Ahmet Kahraman (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2017, Mechanical Engineering

This paper complements recent investigations [Handschuh et al. (2014), Talbot et al. (2016)] of the influences of tooth indexing errors on dynamic factors of spur gears by presenting data on changes to the dynamic transmission error. An experimental study is performed using an accelerometer-based dynamic transmission error measurement system incorporated into a high-speed gear tester to establish baseline dynamic behavior of gears having negligible indexing errors, and to characterize changes to this baseline due to application of tightly-controlled intentional indexing errors. Spur gears having different forms of indexing errors are paired with a gear having negligible indexing error. Dynamic transmission error of gear pairs under these error conditions is measured and examined in both time and frequency domains to quantify the transient effects induced by these indexing errors. These measurements are then compared against the baseline, no error condition, as a means to quantify the dynamic vibratory behavior induced due to the tooth indexing errors. These comparisons between measurements indicate clearly that the baseline dynamic response, dominated by well-defined resonance peaks and mesh harmonics, are complemented by non-mesh orders of transmission error due the transient behavior induced by indexing errors. In addition, the tooth (or teeth) having indexing error imparts transient effects which dominate the vibratory response of the system for significantly more mesh cycles than the teeth having errors are in contact. For this reason, along with the results presented in Talbot et al. (2016), it was concluded that spur gears containing indexing errors exhibit significant deviations from nominal behavior, at both a system and time-domain level.

Committee: Ahmet Kahraman (Advisor); David Talbor (Committee Member) Subjects: Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2013, Mechanical Engineering

In this study, load-independent (spin) power losses of a gearbox operating under dip-lubrication conditions are investigated experimentally. A family of final drive helical gear pairs from an automotive transmission is considered as the example for this investigation. A dedicated gearbox is designed and fabricated to operate a single gear or a gear pair under given speed conditions. The test gearbox is incorporated with a high-speed test bed with power loss measurement capability. A test matrix that consists of sets of tests with (i) single spur, helical gears, or disks with no teeth, and (ii) helical gear pairs of varying gear ratios is executed with three different transmission fluids at various temperatures and immersion depths. Power losses from single gear and gear pair tests at identical operating conditions are compared to break down the total spin loss to its main components, namely gear drag loss, gear mesh pocketing loss, and bearing/seal loss. In addition, the space around the gears within the gearbox will be altered to quantify any influences of enclosures and peripheral shrouds on the spin losses of a rotating gear.

Committee: Ahmet Kahraman Dr. (Advisor); Donald Houser Dr. (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2019, Mechanical Engineering

In this study, a new state-of-the-art gear contact durability test machine is developed to eliminate some key limitations, issues and inconveniences associated with conventional FZG machines. Based on lessons learned from prior in-house studies using conventional FZG machines, a number of requirements are specified. A new four-square concept is designed and fabricated to gain various advantages with respect to foot-print, temperature regulation, and long-lasting auxiliary components. The mechanical layout and out-of-the-loop torque application methodology are described along with the heat management and lubrication systems. Various new safety provisions are highlighted, in addition to a streamlined interim gear inspection procedure during long-cycle contact fatigue tests performed on these new machines. For demonstration purposes, the proposed machines are used to conduct an example contact fatigue test program to evaluate a stress-life curve of ground spur gears made of a typical automotive gear steel. The test procedures, test conditions and the test specimens are described. Various results containing digital images of the gear teeth, surface wear and roughness progression over the fatigue life of the gears are detailed. A detailed statistical analysis is presented to define a stress-life curve and confidence intervals. This example fatigue study confirms the suitability of the new machines to perform high-fidelity gear contact fatigue experiments.

Committee: Ahmet Kahraman (Advisor); David Talbot (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2018, Mechanical Engineering

In this study, a test methodology was developed to induce debris to the gear tooth profiles during the operation of a gear pair. This methodology was applied to a number of spur gear specimens for different types, quantities and sizes of debris particles. The extent of surface damage due to application of debris was documented and related to the sizes, types and quantities of debris applied. A high-speed and high-temperature test machine was used to put gears with varying severity of debris damage through a staged scuffing test to investigate the influence of such damage on scuffing outcome. While selected damage sites monitored during staged scuffing tests did not exhibit any progression to be identified as initiation sites for scuffing failure, gears with no or little debris damage were shown to pass the scuffing test while gears with heavier debris damage scuffed consistently. As such, the results of this study show conclusively that there is a direct correlation between severity of the debris damage and resultant scuffing performance of the gears.

Committee: Ahmet Kahraman (Advisor); David Talbot (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2017, Mechanical Engineering

In this study, an experimental investigation of the effects of tooth surface roughnesses on gearbox power losses is performed. Spur gears with five different surface roughness pairings are considered as specimens. They include (i) gears having hard ground surfaces to serve as the baseline condition, (ii) chemically polished surfaces with isotropic lay, (iii) ground-polished surfaces at roughness amplitudes that are comparable to chemically polished surfaces, (iv) ground-polished surfaces that are rougher than smooth ground-polished surfaces, and (v) a ground surface mating with a ground-polished surface. An efficiency test set-up is used to measure gearbox power losses under these surface conditions within the ranges of transmitted torque, speed and oil inlet temperature. Tests under unloaded conditions were performed to isolate the load-independent power losses and remove them from the loaded tests to determine load-dependent power losses. Several roughness parameters including those defined in relation to the bearing-area curve are quantified for each test to investigate which correlated to power loss. Results indicate that the load-independent losses are not influenced by surface treatments while load-dependent losses increase with increased surface roughness amplitudes. An increase in oil temperature, or decrease in viscosity, is seen to increase the gear mesh friction power loss while reducing rolling power losses of bearings, which appears to neutralize changes to gear mesh power losses.

Committee: Ahmet Kahraman PhD (Advisor); David Talbot PhD (Committee Member) Subjects: Automotive Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2009, Mechanical Engineering

This study consists of experimental studies involving two modes of gear contact fatigue failure: gear pitting (spalling) and gear scuffing. For pitting studies, several materials and surface treatments were investigated at various stress levels. These surface treatments included (i) hobbed and shaved (baseline), (ii) chemically polished, (iii) shot peened and plastic honed, and (iv) ground gears. Pitting fatigue lives of chemically polished gears were greater than those of baseline specimens. Both shot peened and plastic honed gears and ground gears were shown to have greater pitting fatigue lives than baseline gears. The improved pitting fatigue life of ground gears over baseline gears appears related to the improved involute profile shapes of the specimens.For gear scuffing experiments, the standard ISO 14635-1 FZG Scuffing Test was performed on AISI 8620 type A spur gears. These experiments included four uncoated gear pairs and one gear pair coated with an experimental PVD coating. Uncoated gears encountered scuffing during Stages 11 and 12. A high correlation between temperature and scuffing results was detected for both coated and uncoated specimens.

Committee: Ahmet Kahraman PhD (Advisor); Donald Houser PhD (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2009, Mechanical Engineering

The majority of loaded static transmission error test stands developed in the past had little success generating accurate results versus analytical predictions for parallel-axis gearing. Design flaws historically caused issues with speed and torque control, ultimately, leading to erroneous results. Fortunately, some of these issues were corrected through the years, most recently by Schmitkons [1], for loaded transmission error testing of bevel gears sets. The original goal of this thesis was to translate those successes into a test rig for parallel-axis gearing that can measure static transmission error and shaft deflections to take a look at transmission error, shuttling and friction force excitations. However, due to difficulties in achieving a good comparison between experimental results and analytical predictions, the goal was shifted towards simply assessing the performance of the new test stand. By using virtually the same control setup and measurement setup as the loaded bevel gear static transmission error test stand, the new test stand generated static transmission error results for both spur and helical gears at various torque levels. Those results were compared to analytical prediction software codes (WindowsLDP, RomaxDesigner and Helical3D), using optimal and measured micro-geometry topographies. The static transmission error results compared well at low torque values, but deviated from the predicted trends at higher torque values. Ultimately, lessons learned from this test setup will be reflected in future experimental work in order to better assess the accuracy of prediction tools.

Committee: Donald Houser PhD (Advisor); Ahmet Kahraman PhD (Committee Member) Subjects: Engineering