Hybrid propulsion systems for land vehicles

Hybrid propulsion systems for land vehicles have been widely studied for decades, as systems that combine conventional and electric propulsion architectures, with the main aim of fuel consumption and pollution emissions reduction. As far as road vehicles are concerned, both four-wheel vehicles, such as buses or cars, and two wheelers, such as scooters or motorcycles, have been studied, prototyped, and, in some cases, made commercially available. In particular the use of hybrid vehicle for the local transport of passengers or goods is very interesting, due to the growing necessity to have cleaner and more economic transportation systems. In the railways sector the introduction of hybrid propulsion is also possible, in case of small trains with a behaviour similar to urban road vehicles, with mission profiles consisting of frequent acceleration / brakings and stops, for example regional trains used for passengers transport and switching locomotives. In this thesis the studies carried out on the hybrid propulsion system for land vehicles are reported in a systematic way, and the main related issues are discussed. More in detail, in chapter 1 the concept of hybrid propulsion is introduced, definitions and classifications are provided and there are also some examples of their realization listed. Chapter 2 approaches the problem of optimising energy consumption onboard hybrid vehicles in a general way, considering the main issues to be solved in their conceptuality, and therefore often abstracted from the actual structure of the particular drive-train considered. Chapter 3 shows the results of experimental tests carried out on samples of batteries for hybrid-electric vehicles of different technologies (Lead-acid, Nickel Metal Hydride, and Lithium ion) to evaluate their energy efficiencies, when subjected to small cycles like a real operating condition on hybrid vehicles. Chapter 4 describes a hybrid drive train simulation program with a userfriendly man machine interface, developed in Matlab-Simulink™ environment. The program is able to simulate series-hybrid drive trains of either road vehicles or trains. The simulator is certainly a necessary tool in the design phase for the choice of architecture and dimensioning of the various subsystems which to test the energy behaviour of vehicles as a result of different control strategies implemented. Chapter 5 shows the possibility of using hybrid drive-trains for propulsion of small electric trains. The study is based on a project commissioned by Trenitalia (the main Italian rail transport company), regarding regional trains (ALn668) operating in non-electrified lines, and shunter locomotives (D141) operating in the main rail stations. Finally, in chapter 6 the study of a dual-mode propulsion system for railway vehicles is showed; technical and economical analyses of regional passenger dual-mode trains in the Italian railway network are also expounded.