針對四輪轉向車輛高速工況之控制策略開發

Abstract

本研究旨在針對四輪轉向車輛進行高速工況之策略開發，以補充既有四輪轉向系統研究針對高速行駛控制策略之不足，並於改善車輛高速避讓能力之餘同時維持高速穩定性。首先，本研究定義兩種不同之轉向模式，使讓車輛能以斜移式或傳統四輪轉向車輛之形式進行移動。為了確保車輛於低速時之轉向穩定性，控制策略中亦使用阿克曼轉向幾何定義各輪轉角。同時，因車輛行駛過程中可能遭遇許多不確定性，故控制策略加入了以橫擺率作為回授之控制器，確保車輛動態與理想狀態相似。其次，本研究針對兩種轉向模式進行整合，並建立了模式切換之判斷基準。針對模式轉換可能造成車輛出現指向錯誤之情況，本研究開發了一套運用各輪煞車作為作動方式之車頭回正算法，並加入了煞車壓力分配功能以避免各輪胎出現鎖死之情況。最後，本研究將控制策略建立於MATLAB/Simulink環境下，並配合CarSim車輛模擬軟件進行模型在環 (MiL)驗證，以確認所建立控制策略之可行性及其對車輛動態之影響。模擬結果顯示，使用所開發之策略能改善車輛進行高速避讓能力，並同時維持現有四輪轉向車輛之高速穩定性。

In this research, a four-wheel steering control (4WS) algorithm is developed, targeting high-speed driving scenarios to enhance the vehicle’s obstacle avoidance ability and stability. First, tire and vehicle models used in this research are defined. Two steering modes were developed, with one mode determining the steering direction and magnitude of rear wheels similar to the current 4WS, while the other enables diagonal movement of the vehicle. Ackermann Steering Geometry (ASG) is considered in the algorithm. A yaw rate feedback controller is also constructed to ensure proper vehicle motion. Both steering modes are then integrated into a comprehensive control strategy, allowing diagonal moving in lane change maneuvers while maintaining stability in existing 4WS vehicles during high-speed cornering. Additionally, a heading error correction algorithm is constructed to prevent errors during the mode switching process by applying brakes to the required wheel. To prevent lockup on the braking wheel, a brake pressure allocation function is included in the algorithm. Lastly, model-in-the-loop (MiL) validation is performed using joint simulation of MATLAB/Simulink with CarSim software. The results showed that significant improvement was achieved during lane change maneuvers by using the combined strategy. At the same time, stability enhancement on existing 4WS vehicles is retained with the proposed strategy, and heading errors can be rapidly eliminated.