| ASR controls the slip ratio of driving wheels according to a target slip ratio by adjusting the engine torque and applying brake to the spinning wheel. In this way the acceleration performance and stability of the vehicle can be enhanced. The ASR has been equipped on sedans for more than a decade in overseas , however,in our country we are still in reaching phase,but the study on this matter has been carrying out both in Universities and companies.There are several problems to be solved during the study of ASR. The two of them discussed in this thesis are road identification technology and coordinate of throttle control and brake control on driving wheels.The control method for ASR control system widely used today are throttle control , brake control on driving wheels and the combination of throttle control and brake control. Throttle control has a comfort, smooth control effect and slow response; it can control the driving wheels on each side of vehicle symmetrically. Brake control has a faster response but less smooth control effect, but it can control the driving wheels symmetrically and individually. There are not many papers which focus on the coordinate of the two methods, hence how to design feasible control logic to make use of the two to obtain the best control effect are studied.The control effects of modern vehicle anti slip control system mainly depend on the control strategy and control algorithm. Mostly, the anti slip control system are designed to control the slip ratio of each controlled wheels to the target slip ratio. The fact is that the slip ratio where the friction coefficient attains its maximum value can be influenced by several factors. Hence, the road identification technology can directly influence the control effect of anti slip control system. The thesis proposed introduces a new method to estimate the road adhesion coefficient by using the power train model and the acceleration of driving wheels. The simulation results at the end of the thesis show that this method can estimate the road frication coefficient effectively and timely. Based on the identified road adhesion coefficient, a base value of target slip ratio for driving wheel is derived. Then this base vale should be correct according to the reference speed of vehicle. The target driving wheel speed can be calculated for the corrected value of the target slip ratio and the reference vehicle speed.The study on the ASR control logic and algorithm are discussed based on the calculated target driving wheel speed, including the incremental PI controller for throttle control, PID controller for brake control, combined control of incremental PI control of throttle and PID brake control, thresholds setting for ASR control and deactivating logic of ASR.The simulation model is built, including engine model, clutch model, power train model, G.GIM tyre model, model for tyre load and slip angle of each tyre, brake system model and 8 DOFs vehicle dynamic model. The simulation results of ASR control system are analyzed in the fourth chapter. The control logic is validated on several typical road conditions, such as homogenous mue road, split mue road, mue jump road and straight road acceleration. Besides, the simulation results are compared with the results of combined control of incremental PI control and logic threshold braking control under the same condition. The compare results show that the control logic proposed in this thesis has a better control effect.The conclusion and the perspective of this thesis are:1. Road adhesion coefficient identification through power train model and driving wheels'accelerations can estimate the road adhesion coefficient properly; however, the model here should be accurate.2. The control logic and algorithm proposed in this thesis are effective, and it has a better control effect compared with combined control of incremental PI control and logic threshold braking control.
|
PDF Full Text Request