"Through The Road" Hybrid configurations for Service Vehicles: modelling and analysis

In the last decade, Hybrid Electric Vehicles have spread worldwide in passenger cars applications, for their capability to decrease fuel consumption and emissions. However, in the Medium and Heavy Duty market this technology is not as common, while it could represent a valid solution to increase the overall efficiency of these vehicles. Since Heavy Duty vehicles’ lifespan is typically above one million kilometers, and their fuel consumption is much greater than passenger cars’ vehicles, mainly because of their considerable mass and their higher aerodynamic coefficient, it is clear how even a slight increase in efficiency could represent a substantial economic advantage throughout the life cycle of the vehicle. The purpose of this Thesis is to explore the possibilities of electrification for medium/heavy duty service vehicles, and to highlight the advantages that this technology can provide, especially in terms of fuel economy and, therefore, carbon dioxide emissions. Two “Through the Road” HEV configurations will be modeled and evaluated, consisting of a standard Internal Combustion Engine mounted on the front axle and powering two axles of the vehicle, and one or two electric motors mounted on the third rear axle. The term “Through the Road” indicates that the connection between the ICE and the electric motors is provided by the constraints imposed by the road, and not by a mechanical transmission, as it often happens in standard Parallel Hybrid Configurations. Regarding the electric axle, two solutions will be discussed: -??Single electric motor coupled with a differential. In this configuration, an electric motor is coupled through conical gears to the differential crown. This configuration requires an electric motor capable of delivering a relatively low torque at higher speeds. -??Two in-wheel electric motors. In this configuration, two electric motors are directly coupled to the wheels, without gear reductions. The motors are two frameless motors capable of delivering high torque at low speed. The two hybrid configurations will be modeled using “TruckSim” software by “Mechanical Simulations”, coupled with Matlab-Simulink environment. The two configurations and the standard ICE-only layout will be simulated in different real driving scenarios and the results will be compared in order to highlight the behavior of the systems, especially in terms of fuel consumption advantages. Finally, for both configurations, a feasibility study will be conducted. In this phase, different design approaches for the configurations will be discussed. This step is necessary to evaluate whether the solutions could be engineered without any critical issue, or if they have to be previously discarded because of obvious design difficulties.