Browsing by Author "Vaughan, N. D."
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Item Open Access Adhesive and molecular friction in tribological conjunctions(Cranfield University, 2012-01) Chong, William Woei Fong; Teodorescu, Mircea S.; Vaughan, N. D.This thesis investigates the underlying causes of friction and ine ciency within an internal combustion engine, focusing on the ring-liner conjunction in the vicinity of the power-stroke top dead centre reversal. In such lubricated contacts, friction is the result of the interplay between numerous kinetics, with those at micro- and nano-scale interactions being signi cantly di erent than the ones at larger scales. A modi ed Elrod's cavitation algorithm is developed to determine the microscopic tribological characteristics of the piston ring-liner contact. Predicting lubricant tran- sient behaviour is critical when the inlet reversal leads to thin lms and inherent metal-to-metal interaction. The model clearly shows that cavitation at the trailing edge of the ring-liner contact generated pre-reversal, persists after reversal and pro- motes starvation and depletion of the oil lm. Hence, this will lead to boundary friction. A fractal based boundary friction model is developed for lightly loaded asperity con- tacts, separated by diminishing small lms, usually wetted by a layer of molecules adsorbed to the tips of the asperities. In nano-scale conjunctions, a lubricant layering e ect often takes place due to the smoothness of surfaces, which is governed by the surface and lubricant properties. A molecularly thin layer of lubricant molecules can adhere to the asperities, being the last barrier against direct surface contact. As a result, boundary friction (prevailing in such diminishing gaps) is actually determined by a combination of shearing of a thin adsorbed lm, adhesion of approaching as- perities and their plastic deformation. A model for physio-chemical hydrodynamic mechanism is successfully established, describing the formation of thin adsorbed lms between asperities. This model is e ectively integrated with separately devel- oped models that predict the adhesive and plastic contact of asperities.Item Open Access Advanced control concepts for a parallel hybrid powertrain with infinitely variable transmission(Cranfield University, 2006) Cacciatori, E.; Vaughan, N. D.Poweitrain systems of increasing complexity are being introduced by automotive manufacturers in order to reduce carbon emissions into the atmosphere: hybrid electric vehicles and continuously variable transmissions represent effective contributions to achieve the emission reduction target. The increased complexity calls for more sophisticated control strategies to be developed; different energy management approaches have been investigated in the past, in most cases without considering driveability requirements. Those strategies relying on the knowledge of future driving conditions cannot be deployed in a real-time controller and are only used to investigate patterns of optimal behaviour. This Thesis investigates two energy management strategies for an innovative parallel hybrid powertrain concept with innately variable transmission. This was developed as part of a government funded research project aiming at demonstrating the potential fuel economy benefit of such driveline configuration. Both strategies have a common architecture and rely on a common scheme to control the transient vehicle response; this was experimentally calibrated in order to provide improved driveability levels with respect to the conventional non hybrid powertrain deploying the same transmission concept. This control scheme and its calibration are maintained across the two energy management strategies so that consistent vehicle behaviour is achieved and the cost of driveability in terms of energy usage is preserved. The first energy management strategy was heuristically formulated to maximise operation of the single powertrain components in conditions of maximum efficiency. Optimal design techniques were adopted for the calibration of the corresponding rule set. The second strategy formulation was based on the analysis of the simulation results obtained from a dynamic programming model; regression analysis techniques were used to provide the necessary knowledge base required for the control rules formulation and calibration. ln both cases engineering intuition is required for the interpretation of the simulation results and for the individuation of patterns of behaviour. The hybrid powertrain provides consistent fuel economy improvements with respect to the equivalent non hybrid powertrain with innately variable transmission. A driveability appraisal was conducted and the subjective ratings showed an improved overall driveability level of the hybrid powertrain. Despite producing different control and state trajectories, both strategies provide similar fuel economy figures across a set of legislative drive cycles thus demonstrating that both approaches effectively exploit the hardware limits of the powertrain plant.Item Open Access Control of a hybrid electric vehicle with predictive journey estimation(Cranfield University, 2008) Cho, B; Vaughan, N. D.Battery energy management plays a crucial role in fuel economy improvement of charge-sustaining parallel hybrid electric vehicles. Currently available control strategies consider battery state of charge (SOC) and driver’s request through the pedal input in decision-making. This method does not achieve an optimal performance for saving fuel or maintaining appropriate SOC level, especially during the operation in extreme driving conditions or hilly terrain. The objective of this thesis is to develop a control algorithm using forthcoming traffic condition and road elevation, which could be fed from navigation systems. This would enable the controller to predict potential of regenerative charging to capture cost-free energy and intentionally depleting battery energy to assist an engine at high power demand. The starting point for this research is the modelling of a small sport-utility vehicle by the analysis of the vehicles currently available in the market. The result of the analysis is used in order to establish a generic mild hybrid powertrain model, which is subsequently examined to compare the performance of controllers. A baseline is established with a conventional powertrain equipped with a spark ignition direct injection engine and a continuously variable transmission. Hybridisation of this vehicle with an integrated starter alternator and a traditional rule-based control strategy is presented. Parameter optimisation in four standard driving cycles is explained, followed by a detailed energy flow analysis. An additional potential improvement is presented by dynamic programming (DP), which shows a benefit of a predictive control. Based on these results, a predictive control algorithm using fuzzy logic is introduced. The main tools of the controller design are the DP, adaptive-network-based fuzzy inference system with subtractive clustering and design of experiment. Using a quasi-static backward simulation model, the performance of the controller is compared with the result from the instantaneous control and the DP. The focus is fuel saving and SOC control at the end of journeys, especially in aggressive driving conditions and a hilly road. The controller shows a good potential to improve fuel economy and tight SOC control in long journey and hilly terrain. Fuel economy improvement and SOC correction are close to the optimal solution by the DP, especially in long trips on steep road where there is a large gap between the baseline controller and the DP. However, there is little benefit in short trips and flat road. It is caused by the low improvement margin of the mild hybrid powertrain and the limited future journey information. To provide a further step to implementation, a software-in-the-loop simulation model is developed. A fully dynamic model of the powertrain and the control algorithm are implemented in AMESim-Simulink co-simulation environment. This shows small deterioration of the control performance by driver’s pedal action, powertrain dynamics and limited computational precision on the controller performance.Item Open Access A Critique of Laser-Induced Incandescence for the Measurement of Soot(Cranfield University, 2008-10) Smallwood , Gregory J.; Vaughan, N. D.The health and environmental risks due to airborne nanoparticles are important issues facing the citizens and governments of the industrialized countries. To assess and mitigate these risks, increasingly stringent regulations are being enacted to reduce the particulate emissions from the combustion of hydrocarbon fuels, which primarily consist of soot. Improvements to the understanding of the formation of soot nanoparticles and their impact on the health and the environment are required. This necessitates advances in the state of quantitative measurement of soot. Laser-induced incandescence (LII) is an optical diagnostic technique for the measurement of concentration and primary particle diameter of soot with high selectivity. Limitations with conventional LII were identified and a significantly enhanced technique, autocompensating LII (AC-LII), was developed employing time- resolved two-colour pyrometry, low fluence, and an absolute intensity calibration to address these limitations. AC-LII was shown to measure the soot particle temperature and automatically compensate for variations in the measurement environment that affected the peak soot particle temperature. With low fluence, AC-LII was shown to avoid soot sublimation, which impacted the measurements of concentration and size with high fluences. AC-LII was applied to flames and to combustion-generated emissions. At low ambient temperatures it was discovered that the measured concentration varied with fluence. To mitigate this issue, it was recommended that AC-LII be performed at a moderate fluence near the sublimation threshold. In order to assess the impact of distributions of the soot primary particle diameter and of aggregate size, analysis coupling experiments with a state-of-the-art numerical model of the heat transfer was performed. The results showed that AC-LII signal evaluation should begin immediately after an initial anomalous cooling period but before distribution effects become dominant. The sensitivity of AC-LII was optimized and applied to measure atmospheric black carbon concentrations. Comparison to other instruments demonstrated that AC-LII has significant advantages for the measurement of soot, and represents a major advancementin techniques for nanoparticle characterization.Item Open Access Definition and verification of a set of reusable reference architectures for hybrid vehicle development(Cranfield University, 2012) Harrington, Cian; Marco, J.; Vaughan, N. D.Current concerns regarding climate change and energy security have resulted in an increasing demand for low carbon vehicles, including: more efficient internal combustion engine vehicles, alternative fuel vehicles, electric vehicles and hybrid vehicles. Unlike traditional internal combustion engine vehicles and electric vehicles, hybrid vehicles contain a minimum of two energy storage systems. These are required to deliver power through a complex powertrain which must combine these power flows electrically or mechanically (or both), before torque can be delivered to the wheel. Three distinct types of hybrid vehicles exist, series hybrids, parallel hybrids and compound hybrids. Each type of hybrid presents a unique engineering challenge. Also, within each hybrid type there exists a wide range of configurations of components, in size and type. The emergence of this new family of hybrid vehicles has necessitated a new component to vehicle development, the Vehicle Supervisory Controller (VSC). The VSC must determine and deliver driver torque demand, dividing the delivery of that demand from the multiple energy storage systems as a function of efficiencies and capacities. This control component is not commonly a standalone entity in traditional internal combustion vehicles and therefore presents an opportunity to apply a systems engineering approach to hybrid vehicle systems and VSC control system development. A key non-‐functional requirement in systems engineering is reusability. A common method for maximising system reusability is a Reference Architecture (RA). This is an abstraction of the minimum set of shared system features (structure, functions, interactions and behaviour) that can be applied to a number of similar but distinct system deployments. It is argued that the employment of RAs in hybrid vehicle development would reduce VSC development time and cost. This Thesis expands this research to determine if one RA is extendable to all hybrid vehicle types and combines the scientific method with the scenario testing method to verify the reusability of RAs by demonstration. A set of hypotheses are posed: Can one RA represent all hybrid types? If not, can a minimum number of RAs be defined which represents all hybrid types? These hypotheses are tested by a set of scenarios. The RA is used as a template for a vehicle deployment (a scenario), which is then tested numerically, thereby verifying that the RA is valid for this type of vehicle. This Thesis determines that two RAs are required to represent the three hybrid vehicle types. One RA is needed for series hybrids, and the second RA covers parallel and compound hybrids. This is done at a level of abstraction which is high enough to avoid system specific features but low enough to incorporate detailed control functionality. One series hybrid is deployed using the series RA into simulation, hardware and onto a vehicle for testing. This verifies that the series RA is valid for this type of vehicle. The parallel RA is used to develop two sub-‐types of parallel hybrids and one compound hybrid. This research has been conducted with industrial partners who value, and are employing, the findings of this research in their hybrid vehicle development programs.Item Open Access Matching of Internal Combustion Engine Characteristics for Continuously Variable Transmissions(Cranfield University, 2007) Bonnet, Baptiste; Vaughan, N. D.This work proposes to match the engine characteristics to the requirements of the Continuously Variable Transmission [CVT] powertrain. The normal process is to pair the transmission to the engine and modify its calibration without considering the full potential to modify the engine. On the one hand continuously variable transmissions offer the possibility to operate the engine closer to its best efficiency. They benefit from the high versatility of the effective speed ratio between the wheel and the engine to match a driver requested power. On the other hand, this concept demands slightly different qualities from the gasoline or diesel engine. For instance, a torque margin is necessary in most cases to allow for engine speed controllability and transients often involve speed and torque together. The necessity for an appropriate engine matching approach to the CVT powertrain is justified in this thesis and supported by a survey of the current engineering trends with particular emphasis on CVT prospects. The trends towards a more integrated powertrain control system are highlighted, as well as the requirements on the engine behaviour itself. Two separate research axes are taken to investigate low Brake Specific Fuel Consumption [BSFC] in the low speed region and torque transient respectively for a large V8 gasoline engine and a turbocharged diesel V6 engine. This work is based on suitable simulation environments established for both engines in the powertrain. The modelling exercises are aimed at supplying appropriate models that can be validated against experimental data. The simulation platforms developed then allow the investigation of CVT powertrain biased engine characteristics. The V8 engine model in particular benefited from engine and vehicle dynamometer data to validate the model behaviour and the accuracy of the prediction. It benefited from the parallel work conducted on the Electrically Assisted Infinitely Variable Transmission [EASIVT] project in Cranfield University. The EASIVT vehicle is a parallel mild hybrid aimed at demonstrating the combined fuel economy benefits of a CVT technology and hybridisation. From the CVT powertrain requirements for fuel economy, BSFC operation can be further promoted in the low speed region if Noise Vibration and Harshness [NVH] counter-measures are developed. A study of the combustion torque oscillations at the crankshaft led to the elaboration of an Active Vibration Control [AVC] strategy for the hybrid Integrated Motor Generator [IMG]. Successful implementation of the strategy in both simulation and in-vehicle helped quantify the benefits and short comings of engine operation for best fuel economy. The development in parallel of the hybrid control functions for torque assist and regenerative braking made it possible to implement the low speed AVC in the vehicle without a driveability penalty. The V6 TDI model yielded a realistic and representative simulation for the transient torque response improvement research to be undertaken. For that purpose, the model was tuned against full-load data and the air path control sub-systems were designed and calibrated similarly to a real application. The model was able to highlight the turbocharger lag issue associated with a large combined speed and torque transient inevitable in the fuel economy biased CVT powertrain. This study proposes a Manifold Air Injection [MAI] system in the intake of the engine to help breathing when the VGT operating conditions cannot be shifted rapidly enough for a manoeuvre. The system design constraints were analysed and a suitable strategy was elaborated and calibrated. A sensitivity analysis was also conducted to demonstrate the influence of the MAI design and control variables on the engine performance in the CVT powertrain In conclusion, the benefits of the engine characteristic matching were highlighted in both cases. A review of the work achieved is available in the last chapter, including prospects for further improvements and investigations. The ideal engine characteristics for gasoline and diesel engine technologies integrated in a CVT powertrain are derived from the experience gathered in the research and the results obtained from the tests in low speed operation and transient torque control respectively for the gasoline and the diesel engines. The engine characteristics can be altered toward a better match with a CVT by the use of specific hardware and control strategy. This work recommends that a direct injected, variable valve actuated gasoline engine provides the ideal starting point for low fuel consumption powertrain. When integrated within a mild hybrid CVT powertrain, the full benefits are obtained with the use of low speed operation and AVC. If no electrical machine is available to torque assist the engine, then existing supercharging concepts for a downsized engine can be applied. Diesel engines can also be downsized because of their high torque density. Increased turbocharging boost levels allow steady state torque levels to be maintained in the downsizing process. The CVT powertrain can optimise the fuel consumption and emission levels by appropriate selection of the engine steady state operating points. The torque response lag then becomes critical for the CVT to control the engine speed. This can be improved by the use of Manifold air Injection to assist the turbocharger.Item Open Access Modelling and control of a light-duty hybrid electric truck(Cranfield University, 2006-09) Park, Jong-Kyu; Vaughan, N. D.This study is concentrated on modelling and developing the controller for the light-duty hybrid electric truck. The hybrid electric vehicle has advantages in fuel economy. However, there have been relatively few studies on commercial HEVs, whilst a considerable number of studies on the hybrid electric system have been conducted in the field of passenger cars. So the current status and the methodologies to develop the LD hybrid electric truck model have been studied through the literature review. The modelling process used in this study is divided into three major stages. The first stage is to determine the structure of the hybrid electric truck and define the hardware. The second is the component modelling using the AMESim simulation tool to develop a forward facing model. In order to complete the component modelling, the information and data were collected from various sources including references and ADVISOR. The third stage is concerned with the controller which was written in Simulink. This was run in a co-simulation with the AMESim vehicle model. Through the initial simulation, the charge-sustaining performance of this controller was verified and improved. Finally, the simulations for the complete model were carried out over a number of drive cycles, such as CBDTRUCK, JE05, and TRL LGV drive cycle, to evaluate and analyse the effect on the fuel economy and the vehicle performance by the engine operating zone and the EM power capacity. The report presents a comparison of the fuel efficiency of the conventional vehicle and the LD hybrid electric truck. The results obtained by the simulation show the feasibility to build the complete vehicle with the designed controller.