Transient Trajectory Shaping Control Strategy Development for an Autonomous Capable Ground Vehicle

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The vehicle stabilization and safety control have long been major obstacles in the vehicle control system design for autonomous capable vehicles. The objective of this proposed research is to develop a systematic transient control strategy for an autonomous capable ground vehicle to improve the overall vehicle transient performance and safety in adverse conditions. In this research, a Four-Wheel-Independent-Drive (FWID) vehicle structure is adopted. In such a structure, each of the wheels in a ground vehicle can be independently driven, for example, by an in-wheel (or hub) motor. The FWID vehicle is considered to be an effective way of enhancing vehicle driving safety and light weighting. In a FWID vehicle, an additional yaw moment can be generated with torque differences between the left and right wheels to control the vehicle yaw motion. The induced external yaw moment together with the automatic and fast steering action from an active steering system, make it possible to simultaneously regulate the vehicle lateral velocity and track the desired yaw rate. Thus, the vehicle performance, safety, and trajectory capability can be significantly improved. In addition, by using a wheel direct drive structure, the total weight of the vehicle can be substantially reduced due to the simplified transmission system. Although the Four-Wheel-Independent-Drive (FWID) structure can substantially improve vehicle capability, the challenges in control complexity, model uncertainties, and light vehicle weight are still long term issues. In the proposed research, these issues will be solved through the following frames: the vehicle safety boundary in the near future horizon will be modeled based on the vehicle dynamics, driving conditions, and safety buffer; the vehicle transient trajectory will be controlled within the bounds via a trajectory shaping control strategy. To deal with the model uncertainty issue, a combined model-driven and data-driven approach will be used to reconfigure the control-oriented model online and define the safety boundary in real time. For the path tracking control, a novel transient trajectory shaping control strategy, developed in the applicant's prior work, will be further investigated and applied in this research. As some most recent results in the applicant's research group, vehicle side slip angle can be bounded by a pre-defined safety boundary. The safety boundary are determined by real-time estimating the vehicle safe operating region and control actuator constraints. The novelty of the shaping concept in the proposed strategy is not to force the vehicle strictly to follow a desired trajectory. Instead, the additional yaw moment from four wheel actuations will be used to guarantee the vehicle within the safety boundary given the uncertainties while the normal steering.