應用最佳化輪胎與路面間摩擦力分配於車輛運動控制

Abstract

近年來越來越多的國內外汽車大廠都紛紛投入電動車的發展，電動車將會成為未來交通載具新興的發展趨勢，其除了有環保節能的效益外，亦可提供不同的車輛驅動與操控架構，例如：四輪獨立驅動與四輪獨立轉向等等。而基於電動車所提供的驅動與操控架構，可應用更先進的運動控制技術提升車輛的安全性與操控性。 本研究針對四輪獨立驅動與四輪獨立轉向車輛，將運動控制架構分為上、下層控制器，上層控制器計算所需的縱向合力、側向合力與橫擺力矩的總和，使車輛的動態跟隨給定的參考軌跡；下層控制器則考慮輪胎的非線性特性以及與真實輪胎間模型不確定性的問題，藉由控制輪胎力矩與轉向角產生所需的輪胎摩擦力。上層與下層控制器之間透過最佳化摩擦力分配將上層控制器所需之力量適當地分配給每個輪胎，再由下層控制器使各個輪胎產生所需的縱向與側向摩擦力。本研究透過模擬驗證在轉向與車道變換的駕駛情況下控制器控制的結果，在此控制架構下，能夠改善四輪轉向在車輛側向加速度大時對車輛運動控制的不穩定問題，以及彌補直接橫擺力矩控制對車輛側向運動控制的不足。

In this paper, the proposed vehicle motion control structure is separated into the upper controller and the lower controller. The sliding mode control technique is used in the upper controller for calculating the amount of total longitudinal force, lateral force and yaw moment such that the vehicle can track a given reference trajectory. Then the optimum tire force distribution algorithm determines the longitudinal and lateral forces of each tire, subject to the constraints that the resulting forces and moment of all tires meet the requirements of the upper controller, and that the friction ellipse of each tire is satisfied. In the lower controller, a nonlinear Dugoff’s tire model is considered when using sliding mode control technique to generate the assigned tire forces by controlling the wheel torque and the steering angle. Comparisons of the proposed control structure with the four-wheel steering control and direct yaw moment control are conducted by simulations. The results indicate that the proposed structure can improve the handling performance and stability of vehicle motion when the other control methods fail in the event of high lateral acceleration.