Reconfigurable Motion Control Systems for Over-Actuated Road Vehicles

Doktorsavhandling, 2007

Over-actuated systems, such as today's road vehicle configurations, have more motion actuators than controlled motions. For example, a passenger car has a combustion engine and four mechanical brakes, all of which can be used individually to correct any error in yaw rate when the vehicle becomes under- or oversteered. The over-actuation becomes even more obvious when the vehicle is configured with additional motion actuators such as electric motor(s). This is the case for Fuel Cell and Hybrid Electric Vehicles where blending between the use of different actuators is needed. This thesis proposes how a motion control system for over-actuated road vehicles can be made reconfigurable within the context of both offline and online adaptivity. Offline, the proposed control system is easily reconfigured to handle a wide range of vehicle configurations, with different types and numbers of motion actuators, without changing the control law for the desired ground motion of the vehicle. Online, the motion control system adapts its use of the motion actuators to the current conditions of the available actuators and their ability to generate tyre forces on the ground. Another online feature is the smooth arbitration between desired actuator use to both minimize energy consumption and assure vehicle stability. This smooth arbitration is especially important for vehicle configurations which have an energy buffer. The proposed motion control system uses control allocation which separates the control law for the ground motion from the distribution of the desired motion forces among the available actuators for the specific configuration. The optimization formulation of the control allocator considers the actuator limits in both position and rate of change. Through detailed modelling of different vehicle configurations and their actuators, drivetrains, and chassis, it was shown by simulation that the proposed motion control system is both offline and online reconfigurable. The results from different driving manoeuvres showed that the control allocator not only reconfigured the distribution when the actuators were saturated or limited by low road/tyre friction but also ensured that vehicle stability was upheld at all times. This was accomplished by prioritizing vehicle motion higher than energy management in the optimization formulation of the control allocator.