應用四輪轉向於車輛側向運動控制之研究

Abstract

四輪轉向系統具有縮小車輛轉彎半徑與穩定車身側向運動之優點，透過最新之電子控制與感測技術，四輪轉向控制器可隨車輛操控狀況補償前後輪之轉向角，使車輛之側向運動沿著參考軌跡進行，以提高車輛之靈活性與穩定性。 另一方面，市面上所售之ㄧ般汽車在轉向時，所表現出的特性皆為不足轉向(Under Steering)，這是一種利用機械性質所表現出的一種對抗外擾(側風、路面崎嶇等)的手段，但緊急避障的效果不如具中性轉向特性的車輛。因此，將利用四輪轉向(4-wheel steering)系統採用 Output Tracking Control的方式降低外擾對系統的影響，並設計參考模型(Reference Model)使汽車在近似中性轉向(Neutral Steering)以及在減低側滑角(Sideslip angle)的狀況下行駛。 本文之實驗模型車安裝有陀螺儀、加速規、電位計、編碼器等感測器與DSP控制器，以實現四輪轉向控制系統。實驗證實車輛之側滑角(sideslip angle)與橫擺角速度(yaw rate)均能跟隨給定之參考軌跡，外擾亦能有效地抑制。

Four-wheel steering (4WS) systems have advantages over their two-wheel counterparts in terms of smaller turning radii and better stability in vehicle lateral motion. With the aid of latest electronic and sensing technologies, four-wheel steering controllers can compensate for both front wheel angles and rear wheel angles to enhance the maneuverability and stability of the vehicle. On the other hand, most commercial vehicles exhibit understeering properties, which help reject disturbances due to cross-winds and uneven road surfaces. But neutral steering vehicles perform better in object avoidance in emergency cases than understeering vehicles. Therefore, this thesis presents a 4WS control law to reduce the sideslip angle and change the turning characteristics of the vehicle from understeering to nearly neutral steering by means of the H□ output tracking control method and a delicately designed reference model. This experimental vehicle is equipped with gyroscopes, accelerometers, potentiometers, encoders and other sensors as well as the DSP controller to implement the four-wheel steering control system. Experiments confirm that the vehicle sideslip angle and the yaw rate could follow the given reference trajectories, while external interference could be effectively suppressed.