Analyze And Control On Lateral Stability For Tractor Semi-trailer Under Complex Condition

The lateral stability of tractor semi-trailer reduces significantly under complex condition, such as high speed obstacle avoidance under emergency, emergency brake and high speed through the corner, compared to the single unit vehicle, and produces a unique, such as jackknife, drift and even rollover phenomenon, which increases the likelihood of traffic accidents, is the great obstacle in the use of tractor semi-trailer. The number of casualties caused by traffic accidents of tractor semi-trailer is significantly higher than that of other types of vehicles. Therefore, it has important theoretical and practical significance for equipment security and personal safety to analyze the lateral instability mechanism, study the control strategies and methods on lateral stability.The lateral stability of tractor semi-trailer affected by many factors, such as the steering angle of the front wheels, road surface adhesion conditions, vehicle speed, cargo types, the center of gravity and the crosswind. These factors influence each other, and some may be dominant in some cases. Three important factors were studied in this dissertation, and the rollover critical condition of tractor semi-trailer was obtained.Based on the traditional linear model, there influence factors, axle roll steer, tire lateral force compliance steer and Tire aligning moment compliance steer were added into the tire slip angle of there axles. The three degrees of freedom and five degrees of freedom linear model of tractor semi-trailer built with this modified methods still have the advantages of simple structure, small amount of calculation and ease of real-time control, but their performance indicators, the status parameter are closed to the virtual prototype vehicles.For the lateral instability phenomenon of the tractor semi-trailer under complex condition, the traditional solution is to judge the vehicle’s steering type, and then take the appropriate control strategy. The judgement of steering type is mainly based on the yaw rate and sideslip angle. Due to the deformation of suspension and steering system, this judgment has serious limitations. In this dissertation, the axle lateral force saturation was calculated to determine whether the instability phenomenon of sliding, spinning or jackknife arises in the tractor semi-trailer. The tire slip angle, lateral speed, jackknife angle and the road surface normal force and other parameters which are not easy to measure or can not be measured directly will be used in the axis lateral force estimation. Based on the information measured from the lateral acceleration and yaw angular rate sensors in the tractor and semi-trailer, the state observers were used to estimate the tire slip angle, lateral speed and the jackknife angle and then the axis lateral force could be estimated. These parameters play a crucial role the lateral stability control proposed in this dissertation.The estimated axis lateral force saturation was used to determine whether there arises understeer or oversteer in the tractor semi-trailer, the yaw rate only play a supporting role. In the yaw following control the differential braking was used to amend the operating status of the tractor semi-trailer. The rollover index was used in the anti-roll control.The jackknife is prone to appear during high speed through the corners and high speed emergency braking. For the jackknife during high speed through the corners, the control strategy by braking the front outer wheel of tractor and inner wheel of semi-trailer can prevent or reduce the occurrence of jackknife quickly, which is different from the current general method by braking the front outer wheel of tractor and left and right wheels of semi-trailer. Because of the effects of load transfer, the current general method will produce a larger reverse additional torque to offset the anti-jackknife. A fuzzy controller was designed to determine the brake time of anti-lock brake system in this dissertation, according to the vehicle speed and the degree of axle lateral force saturation. For the jackknife phenomenon during the high-speed emergency braking, an apparatus was designed for automatic anti-jackknife. The device will intervente fold trends of tractor semi-trailer due to the emergency brake and prevent the semi-trailer to further yaw increase relative to the tractor.Based on the semi-trailer modal test results, a rigid semi-trailer frame was built. Then the rigid one was flexiblized. Conventionally the semi-trailer was used to be treated as a rigid body in lateral stability control, which differs from the actual situation. Flexible semi-trailer was used to study rollover effect due to the longitudinal torsional deformation of semi-trailer in emergency obstacle avoidance process.