Study Of Vehicle Stablity Based On Direct Yaw Moment Control

With the increased of driving speed and consumers'safety awareness, the safety of vehicles becomes an important research now days. Vehicle stability control (VSC) system is an active safety system, which consists of Anti-lock braking system (ABS), Traction Control System (TCS) and Active Yaw-moment Control system (AYC). A steering wheel angle sensor and a gyro are used to monitor the driving status of vehicle and an expected travel path is confined based on these messages. When it found that, the vehicle has the trend to beyond the expected travel path, VSC will active brake one wheel or two wheels at the same side to retrieve the vehicle to the expected travel path. Different from the passive safety system, such as seat belt and bumper, the active safety system is attend to avoid accident instead of reduce the harm caused by accident. For the available measures of control vehicle's lateral motion is to change the longitudinal forces, the control strategy of VSC is complex. This paper focuses on the control strategy of VSC, and includes the following contents:(1) The following models: 7 degree of freedom (DOF) vehicle model, 2 DOF vehicle model, Dugoff tire model, hydraulic brake model, are adopted to study the dynamics of VSC. And the vehicle dynamics on both high and low friction road are simulated in Matlab/simulink.(2) Analysised the facts which caught vehicle loss the lateral stability, and the effect of yaw rate an side slip angle to vehicle stability; The Direct Yaw-moment Control strategy (DYC) is introduced, and the sliding mode control algorithm is involved to design the DYC and the slip ratio controller.(3) An 8 DOF vehicle model, includes the interference of lateral wind, is built to analysis the influence of lateral wind on vehicle. To overcome the influence, the nonlinear is adopt to design the DYC controller, and a normol DYC controller based on optimal Control is designed for comparison.(4) The feature of side slip angle and the effect of road friction to VSC are studied; a dynamic boundary method is studied, which has two bounds: the upper bound is defined by the limit lateral forces, and the lower bound is the linear bound of vehicle lateral forces. Based on this control threshold, a nonlinear siliding mode controller is designed.(5) Based on the study of road influence on tire side slip angle, the road friction estimation threshold is designed based on tire side slip angle in steering condition. A extened kalman filter is designed for vehicle's longitudinal and lateral velocity estimation, and a neural network algorithm is adopted to design the estimation program.(6) The VSC electronic control unit (ECU) is designed based on ARM7, which program is designed inμC/OS-Ⅱsystem. And a VSC hardware-in-the-loop system is built based on labview.