Stabilisation systems for two-wheeled vehicles

Powered two-wheelers (PTW) are an important class of vehicles that offers significant advantages as compared to cars. However, the possible loss of control, attributed to their intrinsic lateral instability, rises serious concerns on user's safety. This thesis presents an active steering assistant (ActiSA) intended for the lateral stabilisation of PTWs at low speeds. The proposed technology is an alternative to steer-by-wire, which has safety issues related to the removal of the mechanical connection in the steering system, and gyroscopic stabiliser, which tends to be heavy, expensive, and energy-intensive. The work illustrates the development and testing of the ActiSA with its integration in a electric PTW. The ActiSA consists of electro-mechanical system that provides an assistance steering torque along with the rider's input. The prototype features a number of sensors to monitor the vehicle motion. The prototyping demonstrates the possibility to design compact and cheap lateral stabilisation systems for PTWs. Road tests, including lane-change, slalom, multi-frequency steering excitations, and pulse steering excitations, are performed to experimentally identify the steering torque to vehicle lateral dynamics transfer functions. The first focus is on the passive impact of the ActiSA when connected yet inactive, which is associated with the inertia and friction added in the steering. The results show an impact at frequencies below 2Hz, which is particularly evident at low speeds. The second focus is on the identification of a model that captures the main lateral dynamics at low speed. The identified model is suitable for the subsequent control design of the stabiliser. Feedback controllers intended for the lateral stabilisation through the ActiSA are designed using different approaches, namely proportional, H-2, and H-infinity control. Road tests are employed to experimentally assess their stabilisation performance and the impact on the vehicle handling, which should not be significantly altered by the stabiliser. The assistance action is generally perceived as beneficial by the rider. The H-infinity controller shows greater potential in stabilising the vehicle without altering significantly the handling. The results confirm the feasibility of the ActiSA, whose assistance action is effective and with an acceptable effect on handling.