Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains viii, 147 p. : ill. (some col.), maps. Includes abstract. Includes bibliographical references (p. 110-122).

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 459-466). Available also in a digital version from Dissertation Abstracts.

This thesis examines the classic ride comfort vs. handling compromise when designing a vehicle suspension system. A controllable suspension system, that can, through the use of suitable control algorithms, eliminate this compromise, is proposed and implemented. It is a well known fact that if a vehicle suspension system is designed for best ride comfort, then handling performance will suffer and vice versa. This is especially true for the class of vehicle that need to perform well both on- and off-road such as Sports Utility Vehicles (SUV’s) and wheeled military vehicles. These vehicles form the focus of this investigation. The ride comfort and handling of a Land Rover Defender 110 Sports Utility Vehicle is investigated using mathematical modelling and field tests. The full vehicle, non-linear mathematical model, built in MSC ADAMS software, is verified against test data, with favourable correlation between modelled and measured results. The model is subsequently modified to incorporate hydropneumatic springs and used to obtain optimised spring and damper characteristics for ride comfort and handling respectively. Ride comfort is optimised by minimising vertical acceleration when driving in a straight line over a rough, off-road terrain profile. Handling is optimised by minimising the body roll angle through a double lane change manoeuvre. It is found that these optimised results are at opposite corners of the design space, i.e. ride comfort requires a soft suspension while handling requires a stiff suspension. It is shown that the ride comfort vs. handling compromise can only be eliminated by having an active suspension system, or a controllable suspension system that can switch between a soft and a stiff spring, as well as low and high damping. This switching must occur rapidly and automatically without driver intervention. A prototype 4 State Semi-active Suspension System (4S4) is designed, manufactured, tested and modelled mathematically. This system enables switching between low and high damping, as well as between soft and stiff springs in less than 100 milliseconds. A control strategy to switch the suspension system between the “ride” mode and the “handling” mode is proposed, implemented on a test vehicle and evaluated during vehicle tests over various on- and off-road terrains and for various handling manoeuvres. The control strategy is found to be simple and cost effective to implement and works extremely well. Improvements of the order of 50% can be achieved for both ride comfort and handling. AFRIKAANS : In hierdie proefskrif word die klassieke kompromie wat getref moet word tussen ritgemak en hantering, tydens die ontwerp van ‘n voertuig suspensiestelsel ondersoek. ‘n Beheerbare suspensiestelsel, wat die kompromie kan elimineer deur gebruik te maak van toepaslike beheeralgoritmes, word voorgestel en geïmplementeer. Dit is ‘n bekende feit dat, wanneer die karakteristieke van ‘n voertuigsuspensiestelsel ontwerp word vir die beste moontlike ritgemak, die hantering nie na wense is nie, en ook omgekeerd. Dit is veral waar vir ‘n spesifieke kategorie van voertuie, soos veldvoertuie en militêre wielvoertuie, wat oor goeie ritgemak en hantering, beide op paaie en in die veld, moet beskik. Die fokus van die huidige studie val op hierdie kategorie voertuie. Die ritgemak en hantering van ‘n Land Rover Defender 110 veldvoertuig is ondersoek deur gebruik te maak van wiskundige modellering en veldtoetse. Die volvoertuig, nielineêre wiskundige model, soos ontwikkel met behulp van MSC ADAMS sagteware, is geverifieer teen eksperimentele data en goeie korrelasie is verkry. Die model is verander ten einde ‘n hidropneumatiese veer-en-demperstelsel te inkorporeer en verder gebruik om optimale veer- en demperkarakteristieke vir onderskeidelik ritgemak en hantering te verkry. Ritgemak is geoptimeer deur in ‘n reguit lyn oor ‘n rowwe veldterreinprofiel te ry, terwyl hantering geoptimeer is deur ‘n dubbelbaanveranderingsmaneuver uit te voer. Die resultaat is dat die geoptimeerde karakteristieke op die twee uiterstes van die ontwerpsgebied lê. Beste ritgemak benodig ‘n sagte suspensie terwyl beste hantering ‘n harde suspensie benodig. Daar word aangedui dat die ritgemak vs. hantering kompromie slegs elimineer kan word deur gebruik van ‘n aktiewe suspensiestelsel, of ‘n beheerbare suspensiestelsel wat kan skakel tussen ‘n sagte en stywe veer, asook hoë en lae demping. Dié oorskakeling moet vinnig en outomaties geskied sonder enige ingryping van die voertuigbestuurder. ‘n Prototipe 4 Stadium Semi-aktiewe Suspensie Stelsel (4S4) is ontwerp, vervaardig,getoets en wiskundig gemodelleer. Die stelsel skakel tussen hoë en lae demping, asook tussen ‘n stywe en sagte veer binne 100 millisekondes. ‘n Beheerstrategie wat die suspensiestelsel skakel tussen die “ritgemak” en “hantering” modes is voorgestel, op ‘n toetsvoertuig geïmplementeer en evalueer tydens voertuigtoetse oor verskeie pad- en veldry toestande, asook tydens omrol- en hanteringstoetse. Die beheerstrategie is koste-effektief en maklik om te implementeer en werk besonder goed. Verbeterings in die orde van 50% kan behaal word vir beide ritgemak en hantering. / Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

Thesis (M.S.)--University of Nevada, Reno, 2005. / "August 2005." Includes bibliographical references (leaves 48-54). Online version available on the World Wide Web.

Thesis (Ph.D.) -- University of Rhode Island, 2009. / Typescript. Includes bibliographical references (leaves 125-135).

Thesis (M.S.)--University of Montana, 2005. / Includes bibliographical references (leaves 64-70). Also available on the World Wide Web.

Thesis (M.S.)--University of Montana, 2005. / Title from PDF file as viewed on 5/17/2007. Includes bibliographical references (leaves 64-70). Also available in print.

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Thesis (M.Eng.(Mechanical and Aeronautical Engineering))--University of Pretoria, 2008. / Includes bibliographical references.

Currently, in the United States, on-road vehicles are primarily powered by petroleum fuels (gasoline and diesel). These vehicles have caused serious climate change effects from emissions of greenhouse gas (GHG) and health and environmental impacts from criteria air pollutant (CAP). The recent success of shale gas development has brought industry interest in using natural gas to power on-road vehicles. In addition to low costs and wide availability of this national fuel source, natural gas is a common feedstock to produce alternative fuels. The question arises of whether using natural gas for transportation could help or hinder the environment. In this dissertation, I study the economic and environmental effects of a wide range of natural gas fuel pathways for a selection of light duty (LDV) and medium and heavy duty (MHDV) vehicle types. I choose to focus on two environmental metrics: GHGs and CAPs emitted over the life cycle of each potential pathway for natural gas use. First in Chapters 2 and 3, I use life-cycle analysis to understand the emissions of GHGs from different natural gas pathway for LDVs and MHDVs. Then in Chapter 4 I focus on the CAP emissions from these vehicles. Overall, I find that none of the natural gas pathways eliminate life cycle air emissions. In fact, only a few pathways reduce life cycle GHG emissions and/or life cycle air pollution damages compared to baseline petroleum fuels (gasoline for light-duty vehicles (LDVs) and diesel for heavy-duty vehicles (HDVs)). For the cases of light duty vehicles (LDVs) and transit buses, battery electric vehicles (BEVs) powered by natural gas-based electricity provide significant reduction in life cycle GHG emissions and life cycle air pollution damages (for almost all counties) compared to the baseline petroleum fuels. However, the actual electricity that charges BEVs may not be natural gas-based electricity in most parts of the U.S. When powered by U.S. grid electricity (using average emission factors for 2010 and 2014), BEVs reduce life cycle GHG emissions to a lesser extent but increase life cycle air pollution damages significantly. Compressed natural gas (CNG), while reducing GHG emissions and CAP emissions (except CO) at tailpipe, are more likely to increase life cycle GHG emissions and increase life cycle air pollution damages in the majority of U.S. counties. For heavy-duty trucks, CNG sparking-ignition (SI) trucks and liquefied natural gas (LNG) high-pressure direct ignition (HPDI) trucks have mixed environmental impacts. While they are unlikely to reduce life cycle GHG emissions compared to diesel, they reduce life cycle air pollution damages in 76-99% of U.S. counties for local-haul tractor-trailers and in 32-71% of U.S. counties for long-haul tractor-trailers. In Chapters 5 and 6, I examine the economic impacts of natural gas fuel pathways for two vehicle types, tractor-trailers and transit buses. I study the economic feasibility of a national natural gas refueling infrastructure for long-haul trucks in U.S., which is a prerequisite for natural gas tractor-trailers. I find that a transition to natural gas fuels in long-haul trucks is more expensive when the shares of natural gas trucks are below 5% because of low refueling demands and over-capacity of the refueling infrastructure to ensure network coverage. At higher shares of natural gas trucks, both the total refueling capacity and the net economic benefits of the national refueling infrastructure increase almost linearly as adoption increases. Finally, in Chapter 6, I provide an economic-technology assessment for transit buses by considering both life cycle ownership costs and life cycle social costs due to GHG emissions and CAP emissions. Transit buses are early adopters of alternative fuel technologies because of funding supports and operation characteristics (such as high fuel consumption and private refueling infrastructure). I find that the availability of external funding is crucial for transit agencies to adopt any alternative fuel option. Without external funding, only rapid-charging battery electric buses (BEBs) have lower ownership & social costs than conventional diesel buses. When external funding is available to reduce bus purchase costs by 80%, BEBs become much more cost-effective. In this case, life cycle ownership and social costs of BEBs are 37-43% lower than conventional diesel buses. Including life cycle social costs does not change the ranking of alternative fuel options. The findings in this dissertation suggest different strategies of using natural gas for different vehicle markets. Natural gas is best used in electric power generation than to produce gaseous or liquid fuels for powering on-road LDVs. The use of CNG and LNG for heavy-duty trucks may continue as there are less alternative fuel options but issues such as methane leakage should be addressed to avoid important climate change effect. Finally, natural gas-based transportation fuels can at best partially mitigate climate change or air pollution damages, so other mitigation strategies in the transportation sector are ultimately needed to achieve sustainable transportation.