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

车辆稳定性和安全控制一直是自主车辆控制系统设计中的主要障碍。这项研究的目的是开发一个系统的瞬态控制策略，自主能力的地面车辆，以提高整体车辆的瞬态性能和安全性在不利条件下。在本研究中，四轮独立驱动（FWID）的车辆结构被采用。在这种结构中，地面车辆中的每个车轮可以例如由轮内（或轮毂）马达独立地驱动。FWID车辆被认为是提高车辆行驶安全性和轻量化的有效途径。在FWID车辆中，可以利用左右轮之间的扭矩差来产生附加横摆力矩，以控制车辆横摆运动。感应的外部横摆力矩与来自主动转向系统的自动和快速转向动作一起，使得可以同时调节车辆横向速度并跟踪期望的横摆率。因此，车辆性能、安全性和轨迹能力可以显著提高。此外，通过使用车轮直接驱动结构，由于简化的传动系统，车辆的总重量可以大大降低。 虽然四轮独立驱动（FWID）结构可以大大提高车辆的性能，但控制复杂性，模型不确定性和车辆重量轻的挑战仍然是长期的问题。在所提出的研究中，这些问题将通过以下框架来解决：在不久的将来地平线的车辆安全边界将建模的基础上的车辆动力学，驾驶条件，和安全缓冲器;车辆瞬态轨迹将通过轨迹成形控制策略控制在边界内。为了处理模型不确定性问题，将使用模型驱动和数据驱动相结合的方法来在线重新配置面向控制的模型，并真实的实时定义安全边界。对于路径跟踪控制，一种新的瞬态轨迹成形控制策略，在申请人的先前工作中开发的，将进一步研究和应用在本研究中。作为申请人的研究小组中的一些最新结果，车辆侧滑角可以由预定义的安全边界限制。通过实时估计车辆安全运行区域和控制执行器约束来确定安全边界。 在所提出的策略中，成形概念的新奇不是迫使车辆严格地遵循期望的轨迹。相反，来自四个车轮驱动的附加横摆力矩将用于保证车辆在正常转向时的不确定性下处于安全边界内。

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.