Mechanical Engineering - Theses
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ItemComputer simulation and practical evaluation of heavy vehicle performance and fuel economy( 1986)This thesis develops and presents optimisation methodology for heavy vehicle performance and fuel economy. The nature of research undertaken involves both computer simulation and practical evaluation. It is believed that these research components will enable the formulation of proposals supportive to the implementation of a heavy vehicle fuel conservation programme. The research commences with a review of heavy vehicle travel and fuel usage statistics relative to those of other road users. Heavy vehicles are then categorised according to their configuration and area of operation. This categorisation, which is based on the Australian Bureau of Statistics 1982 motor vehicle survey, serves as the principle criterion for the development of driving cycles representative of heavy vehicle driving patterns in urban and non-urban areas. Traffic data collection methods and various means for the translation of data into a representative speed-time trace (driving cycle) are reviewed and evaluated. Four comprehensive field surveys conducted over selected routes using an instrumented car to follow and record the driving patterns of targetted heavy vehicles are detailed. Synthesis of four driving cycles follows. These cycles provide means for the study of vehicle performance and fuel economy by giving instructions to a driver or computer on how to operate a vehicle over a given distance or period of time. The application of TARCYC, a comprehensive software package, developed to support data acquisition and reduction, and to implement an enhanced microtrip accumulation technique, is described. It is shown that application of this package leads to the development of very realistic driving cycles with a minimal statistical similarity of 94% to the target data. Vehicle proving ground and highway tests are described. The tests allowed the collection of a large data base for a vehicle with varying configurations. A test procedure providing fuel economy information for a baseline vehicle and for a modified configuration is developed and demonstrated. It is also shown that a repeatability band within 1% is achievable. The equipment and instrumentation used and the computer programs developed for data reduction and processing and for the derivation of such vehicle component characteristics as aerodynamic drag and rolling resistance coefficients are described. An account is given of a novel approach which applies a simulation model in conjunction with curve fitting in coastdown analysis. The procedure and format used in archiving the collected data for future research work is also detailed. Modelling of vehicle performance and fuel consumption, using computer programs, commences with a review of HEVSIM, the US Department of Transport model translated to Fortran 77 and adapted by the author for operation on the University of Melbourne VAX/VMS main-frame computer. The simulation capabilities and limitations of this model are assessed and a critical review of 10 other models is also undertaken. Subsequently, the development of TABESAM, a multi -purpose simulation model which incorporates varying levels of complexity and requires only simple input to provide detailed output, is traced. This model can be used for driving cycle analysis, driver training and motivation, vehicle tests, engine mapping and vehicle component optimisation and has been subjected to experimental validation. When compared with transient and steady state test results, the model shows a prediction accuracy in excess of 95%. The model has been adopted by the Society of Automotive Engineers (SAE-A) for deployment in showroom, point of sale decision making contexts and in the Society’s fuel conservation programme. Finally, and as a result of the practical evaluation and computer simulation of heavy vehicle performance and fuel economy, it is concluded that driver training and motivation, vehicle configuration matching to duty cycle and vehicle component optimisation are essential to fuel conservation. It is also maintained that a heavy vehicle fuel conservation programme depends for its success on the involvement and contributions of government bodies, vehicle designers, city and urban planners and owner/operators.