An Investigation Of Vehicle Anti-lock Braking System Based On Slip-ratio

Anti-lock Braking system (ABS) has important significance for improving the active safety of vehicle, economizing money and alleviating damage induced by accidents, so ABS has broad future. The optimal Anti-lock Braking system combining with vehicle dynamics control, which can keep slip-ratio optimal and stable, is an ideal ABS control system. The key technologies of ABS based on slip-ratio consist of processing of wheel speed and calculation of wheel acceleration, estimation of vehicle velocity, estimation of the optimal slip-ratio, and the control strategy of ABS. In order to improve the performance of conventional ABS, the above mentioned key technologies and corresponding realization algorithms had been investigated in this paper, and the ABS product equipped in vehicle for performance test had been manufactured.The research scope of this paper includes:(1) According to the vehicle motion parameters, the 9 degrees of freedom vehicle brake model has been established by utilizing Newtonian mechanics, which can be reduced step by step to a double-wheel vehicle brake model and to a single-wheel vehicle brake model. On the basis of comparing a few kinds of tire models accepted widely, the Magic Formula tire model is selected as the tire model in the vehicle brake model.(2) The acquisition and pre-process of wheel speed signal have been described, and the measurement error of wheel speed signal has been investigated. The main factor which influences the wheel speed threshold is the trigger error whose variation with the wheel speed has been measured by experiment. The calculation method of converting equal-angle sample signal into equal-period sample signal has been surveyed, and the filter technology of wheel speed signal has been realized. An estimation algorithm based on FIR filter to calculate wheel acceleration has been proposed, which is optimal in the sense of minimizing the error variance and its filter coefficient and length have been solved.(3) The estimation method based on multi-sensor fusion has been surveyed. By using the wheel speed signals and vehicle body acceleration signal, the system state equations and measurement equations have been implemented, and the vehicle velocity is estimated by Kalman Filter technology. In order to reduce the calculation work and increase the reliability of system, this paper applies the technology of Median Filter to the four wheel speed signals, and proposes a kind of practical method for calculating vehicle velocity. The trial results verified the feasibility and validity of this method.(4) On the basis of comparing current technologies of road identification, an estimation method of optimal slip-ratio, based on approximate parameters ofμ-λ function, has been proposed. In order to track the abrupt change of road surface, a road surface change monitor based on CUSUM algorithm has been illustrated.(5) By considering wind resistance and wheel rolling resistance in vehicle single wheel brake model, the control technology of realizing the shortest brake distance has been studied by utilizing the optimal control theory, and the shooting methods based on initial variable guess technique has been provided to realize numerical calculation. The adaptive sliding mode variable structure based on model has been studied and been improved further, and its application in slip-ratio based ABS has been realized. The ABS parameter adaptation sliding mode variable structure has been simulated and tested on real vehicle.(6) The hardware and software designs of ABS system, which consist of wheel signal processing circuit and its simulation and verification, vehicle acceleration sensor measurement circuit and DSP application circuit, have been illustrated. An ABS real-time loop experiment platform, on which the validity and feasibility of ABS parameter adaptive sliding mode control method proposed in this paper were verified, has been designed. The road experiment has been realized by the development of ABS product.The above-mentioned investigations have definite reference values and practical meanings for developing our own ABS and exploring theoretical and technical study of vehicle active safety farther.