Direct and Steering Tilt Robust Control of Narrow Vehicles

Narrow tilting vehicles (NTVs) are the convergence of a car and a motorcycle. They are expected to be the new generation of city cars considering their practical dimensions and lower energy consumption. However, due to their height-to-breadth ratio, in order to maintain lateral stability, NTVs should tilt when cornering. Unlike the motorcycle, where the driver tilts the vehicle himself, the tilting of an NTV should be automatic. Two tilting systems are available, i.e., direct tilt control (DTC) and steering tilt control (STC), the combined action of these two systems being certainly the key to considerably improve NTV dynamic performances. In this paper, multivariable control tools (H₂ methodology) are used to design, in a systematic way, lateral assistance controllers driving DTC, STC, or both DTC/STC systems. A three-degree-of-freedom (DoF) model of the vehicle is used, as well as a model of the steering signal, leading to a two-DoF low-order controller with an efficient feedforward anticipative part. Taking advantage of all the available measurements on NTVs, the lateral acceleration is directly regulated. Finally, a gain-scheduling solution is provided to make the DTC, STC, and DTC/STC controllers robust to longitudinal speed variations.