This work proposes to match the engine characteristics to the requirements ofthe Continuously Variable Transmission [CVT] powertrain. The normal process is topair the transmission to the engine and modify its calibration without considering thefull potential to modify the engine. On the one hand continuously variable transmissionsoffer the possibility to operate the engine closer to its best efficiency. They benefit fromthe high versatility of the effective speed ratio between the wheel and the engine tomatch a driver requested power. On the other hand, this concept demands slightlydifferent qualities from the gasoline or diesel engine. For instance, a torque margin isnecessary in most cases to allow for engine speed controllability and transients ofteninvolve speed and torque together. The necessity for an appropriate engine matchingapproach to the CVT powertrain is justified in this thesis and supported by a survey ofthe current engineering trends with particular emphasis on CVT prospects. The trendstowards a more integrated powertrain control system are highlighted, as well as therequirements on the engine behaviour itself.Two separate research axes are taken to investigate low Brake Specific FuelConsumption [BSFC] in the low speed region and torque transient respectively for alarge V8 gasoline engine and a turbocharged diesel V6 engine. This work is based onsuitable simulation environments established for both engines in the powertrain. Themodelling exercises are aimed at supplying appropriate models that can be validatedagainst experimental data. The simulation platforms developed then allow theinvestigation of CVT powertrain biased engine characteristics.The V8 engine model in particular benefited from engine and vehicledynamometer data to validate the model behaviour and the accuracy of the prediction. It benefited from the parallel work conducted on the Electrically Assisted InfinitelyVariable Transmission [EASIVT] project in Cranfield University. The EASIVT vehicleis a parallel mild hybrid aimed at demonstrating the combined fuel economy benefits ofa CVT technology and hybridisation. From the CVT powertrain requirements for fueleconomy, BSFC operation can be further promoted in the low speed region if NoiseVibration and Harshness [NVH] counter-measures are developed. A study of thecombustion torque oscillations at the crankshaft led to the elaboration of an ActiveVibration Control [AVC] strategy for the hybrid Integrated Motor Generator [IMG].Successful implementation of the strategy in both simulation and in-vehicle helpedquantify the benefits and short comings of engine operation for best fuel economy. Thedevelopment in parallel of the hybrid control functions for torque assist and regenerativebraking made it possible to implement the low speed AVC in the vehicle without adriveability penalty.The V6 TDI model yielded a realistic and representative simulation for thetransient torque response improvement research to be undertaken. For that purpose, themodel was tuned against full-load data and the air path control sub-systems weredesigned and calibrated similarly to a real application. The model was able to highlightthe turbocharger lag issue associated with a large combined speed and torque transientinevitable in the fuel economy biased CVT powertrain. This study proposes a ManifoldAir Injection [MAI] system in the intake of the engine to help breathing when the VGToperating conditions cannot be shifted rapidly enough for a manoeuvre. The systemdesign constraints were analysed and a suitable strategy was elaborated and calibrated.A sensitivity analysis was also conducted to demonstrate the influence of the MAIdesign and control variables on the engine performance in the CVT powertrainIn conclusion, the benefits of the engine characteristic matching werehighlighted in both cases. A review of the work achieved is available in the last chapter,including prospects for further improvements and investigations. The ideal enginecharacteristics for gasoline and diesel engine technologies integrated in a CVTpowertrain are derived from the experience gathered in the research and the resultsobtained 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 towarda better match with a CVT by the use of specific hardware and control strategy.This work recommends that a direct injected, variable valve actuated gasolineengine provides the ideal starting point for low fuel consumption powertrain. Whenintegrated within a mild hybrid CVT powertrain, the full benefits are obtained with theuse of low speed operation and AVC. If no electrical machine is available to torqueassist the engine, then existing supercharging concepts for a downsized engine can beapplied.Diesel engines can also be downsized because of their high torque density.Increased turbocharging boost levels allow steady state torque levels to be maintained inthe downsizing process. The CVT powertrain can optimise the fuel consumption andemission levels by appropriate selection of the engine steady state operating points. Thetorque response lag then becomes critical for the CVT to control the engine speed. Thiscan be improved by the use of Manifold air Injection to assist the turbocharger.
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