Interest in hybrid electric vehicles (HEVs) and electric vehicles (EVs) has\ud increased rapidly over recent years from both industrial and academic viewpoints\ud due to increasing concerns about environmental pollution and global oil usage. In\ud the automotive sector, huge efforts have been invested in vehicle technology to\ud improve efficiency and reduce carbon emissions with, for example, hybrid and\ud electric vehicles. This thesis focuses on one design area of these vehicles – the\ud transmission – with the aim of investigating the potential benefits of improved\ud transmissions for HEVs and EVs.\ud For HEVs, a novel transmission developed by Nexxtdrive based on a twin\ud epicyclic design is analysed using a matrix method and its performance is\ud compared with the more common single epicyclic arrangement used successfully\ud in the Toyota Prius. Simulation models are then used to compare the performance\ud of a typical HEV passenger car fitted with these two transmissions over standard\ud driving cycles. The conclusion is that the twin epicyclic offers substantial\ud improvements of up to 20% reduction in energy consumption, though the benefits\ud are sensitive to the driving cycle used.\ud For EVs, most designs to date have used a single fixed ratio transmission, and\ud surprisingly little research has explored whether multi-geared transmissions offer\ud any benefits. The research challenge is whether it is possible to optimise the\ud usage of the electric motor in its region of high efficiency by controlling the\ud transmission. Simulation results of two EV examples confirm that energy\ud consumption benefits are indeed achievable – of between 7 and 14% depending\ud on the driving cycle.\ud Overall, the original aspects of this work – the analysis and modelling the twin\ud epicyclic gearbox; the analysis and modelling the twin epicyclic system in a vehicle\ud and a comparison of the results with single epicyclic system; and the analysis and\ud modelling of EVs with and without a transmission system of varying levels of\ud complexity – have shown that there are worthwhile performance benefits from\ud using improved transmission designs for low carbon vehicles
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