A very stringent problem in most of European cities is the individual mobility. This problem is mainly caused by traffic jam and arising from this are two particularly interesting environmental issues: pollution and noise [1]. Use of two wheeler vehicles does not represent the final solution to these problems, nevertheless they can supply a useful aid to ease them. Recently, two stroke engines are being replaced with four stroke engines. For small capacity engines this means a true reduction in exhaust emissions, especially unburned hydrocarbons (HC), but, on the other hand it involves a performance reduction, particularly for sudden accelerations, which constitute an essential requirement for these vehicles [2, 3, 4, 5]. Hybridisation can help to fill the gap between two stroke engines and cleaner, but less performing four stroke engines [6]. At the same time, it can help to lower fuel consumption, by means of a reduction in the revolution speed [2, 5].
This paper presents a study on a parallel hybrid scooter prototype from the point of view of a better matching between the characteristics of the internal four stroke combustion engine and of the electric motor. Wave fluid-dynamic 1D code was used in order to create a model of the internal combustion engine. The model validation was carried out by the comparison between the simulation results and the experimental data obtained with the roller test bench. Then, some modifications were analysed in order to optimise the behaviour of the engine at a lower revolution speed of the engine, thus diminishing the specific fuel consumption of the vehicle. Finally, such modifications were introduced in a Simulink (Matlab) model to evaluate their influence on the behaviour of the whole hybrid vehicle when running on different road cycle tests.