Intelligent vehicle motion control
This thesis investigates the principle of co-ordination of chassis subsystems by proposing a new control structure for co-ordinating active steering technologies and a brake based directional stability controller. A non-linear vehicle handling model was developed for this study using the Mattab and Simulink tools. This consists of a 4 degree of freedom (d. o. f) lumped-parameter model that includes longitudinal, lateral, yaw and roll motions with quasi-static longitudinal load transfer effects including non-linear suspension and tyre descriptions. The non-linear vehicle dynamics are discussed for the whole operating regime and two specific driving tasks are identified, steerability and stability. In the context of the vehicle states these are yaw rate control and side slip angle bounding respectively. Linear active steering controllers for front, rear and four wheel steering are designed and evaluated in the context of the vehicle handling problem throughout the non-linear operating regime to assist the driver in the two driving tasks previously defined. It is shown through the analysis of the vehicle dynamics in the Chapter 3 that linear controllers can be used to significantly improve the handling behaviour of a non-linear vehicle when only one active input is considered, however when controlling two active inputs, non-linear multivariable approach is required to deal with the strongly coupled nature of the vehicle handling with respect to front and rear steering inputs. A brake based stability system that reflects the state of the art is implemented. The work then proposes a novel co-ordination controller structure for coordination of an active steering controllers and a brake based stability controller for improving to vehicle handling control. The controller was assessed both in steady state and transient tests selected to simulate real world driving manoeuvres over the whole non-linear vehicle handling regime. The co-ordination controller is found to lead to a trade-off between stability and limit cornering performance. The proposed structure improves vehicle stability and reduces interactions in the longitudinal vehicle motion. A detailed discussion of the implications of a coordinated control approach showing it to be a powerful tool providing, the interactions can be conveniently related vehicle handling task and that an appropriate measure of vehicle performance is available. The limitations of the approach are discussed. The most significant limitations being a) the difficulty in proving the optimalty of a heuristic control structure, b) the difficult in assessing the controller behaviour and its interaction with a real driver and c) the likely complexity of the rule base for coordinating more than 2 or 3 systems or describing more complex interactions than were observed here.