應用四輪轉向控制於車輛側向穩定及防止翻覆

Abstract

在現今單一車輛車禍事件中，大部分原因來自於緊急情況行駛時車子發生打滑或翻覆，其中翻覆事故往往造成嚴重的傷亡。為了防止打滑或翻覆，同時提高車輛的操控性，本論文利用四輪轉向系統可縮小車輛轉彎半徑與穩定車身側向運動之優點，設計四輪轉向控制系統，使車輛於緊急駕駛情況仍能保持穩定地行駛，保障駕駛者生命安全。 為了探討四輪轉向車輛於側向、橫擺以及側傾方向運動控制，本論文建立三個自由度線性車輛模型，利用LQG控制理論設計控制器，使系統在模型不準確性與量測雜訊影響下，仍能抑制車身側滑角以防止車子打滑，橫擺角速度跟隨給定的參考訊號，維持車子的轉向能力，另外加入物理限制避免橫擺角速度參考訊號超過車輛運動的物理極限而造成車輛翻覆。 最後本研究以CarSim軟體中高質心休旅車模擬緊急駕駛情況，並通過ISO3888-1測試驗證系統效能。模擬結果顯示本論文所提出之四輪轉向控制系統的確能夠使車輛跟隨駕駛者的轉向命令，同時抑制車身側滑角與避免車輛翻覆。

Four-wheel steering systems have advantages over their two-wheel counterparts in terms of smaller turning radii and better stability in vehicle lateral motion. According to the advantages, this paper presents a four-wheel-steering control system to improve vehicle lateral stability and prevent rollover in emergency driving situations. This study designs an LQG servo controller based on a three degree-of-freedom vehicle model which consists of the lateral, yaw and roll dynamics. The controller commands front and rear steering angles to suppress the sideslip angle, and to track the reference yaw rate signal such that the desired vehicle handling characteristics are achieved. Moreover, vehicle rollover is prevented by limiting the maximum reference yaw rate signal based on a rollover index. The results of emergency driving simulations and the ISO3888-1 test by CarSim HCGSUV model confirm that the vehicle sideslip angle could be suppressed and the vehicle rollover could be prevented without degrading the vehicle’s handling performance.