Active Limit Handling for Enhanced Passenger Vehicle Safety

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Road traffic injuries have become a leading cause of death globally accounting for 1.2 million deaths annually, and will rise in worldwide rank to sixth place as a major cause of death (including decease), by 2020. It is encouraging that, despite the constant increase of the number of vehicles in Europe during the last decade, the number of fatalities demonstrates a slow decay. This can be partly attributed to the enormous improvements in vehicle safety, through the introduction of both passive and active safety systems. By no means, however, have the current state-of-the-art of vehicle safety systems proven adequate to radically reverse the sober traffic accident statistics.Current active safety systems, such as the Electronic Stability Control (ESC), aim at restricting the operation of the vehicle within a region characterised by an on-demand linear increase of tyre forces, away from the tyre's maximum force capacity, allowing the average driver to maintain control of the vehicle. With this project we wish to explore the benefits of using the whole of the available performance of the vehicle, rather than restricting its response, in accident avoidance situations. We propose the development of novel control algorithms, which will use the control authority introduced by current active safety systems and modern power/drive-train configurations, and employ expert driving skills to actively assist the driver exploit the limits of handling of the vehicle during emergency manoeuvring. MIRA, one of the world's leading independent providers of vehicle product engineering, testing, certification and research, has expressed their great interest in exploring the limits of the handling capacity of vehicles with modern power/drive-train configurations and the potential benefits in active safety. The company has agreed to offer their support to this project by means of technical consultation and active participation in the management and execution of the proposed research tasks.Current drive-by-wire (DBW) actuators have allowed for a considerably enhanced control authority over the vehicle, as compared to traditional steering, brake and power/drive-train systems. The human operator provides commands through the conventional controls, that is, the steering wheel, and the throttle and brake pedals, whereas, for instance, the ESC allows for individual wheel braking, and electric motors in hybrid vehicles allow for individual wheel torque control. Race drivers have developed expert techniques to exploit most of the available force capacity of the tyres using the traditional controls. The enhanced control authority provided by modern vehicle controls potentially allows for even more efficient use of the available tyre performance. In this work we wish to explore the performance limits of modern vehicles equipped with DBW actuators, and identify optimum operating conditions related to accident avoidance. The first research task of the proposed work is to obtain steady-state cornering conditions at the limit of handling of the vehicle, that is, in a region of vehicle operation where the tyres produce forces close to their maximum capacity. As a case study we will consider the power/drive-train configuration of MIRA's prototype hybrid vehicle (H4V) which uses two high-torque independently controlled electric motors to drive the rear wheels. Consequently, we will design controllers using linear and nonlinear control design tools, which will stabilise the vehicle in potentially unstable driving conditions, instead of restricting the vehicle in a stable operating region away from its performance limits, using DBW control inputs. The control design will be implemented in a high fidelity simulation environment using experimentally validated vehicle models provided by MIRA. The implementation strategy entails the detection of emergency situations and accounts for the driver's intention.