Research Of Hydraulic ABS Control Algorithm Based On Slip Ratio

ABS(Anti-lock Braking System) is a wide applied automobile active safety technology, which can prevent wheel from locking up even in hard intensity brake and offer improved vehicle control, so that driver can effectively take an avoiding action to protect against accidents. Lots of researches have been done home and abroad on this field, and nowadays, how to improve the system stability and decrease the system overshoot based on modern control theory is one of the most significant development trend.This research is conducted based on BESTURN B70 made by FAW CAR, and one of the purposes of the research is to design a control algorithm of hydraulic ABS based on slip ratio; Off-line and Hardware-in-the-loop simulation is carried out according to National Standard GB/T 13594-2003. Simulation results prove that the above mentioned control algorithm can conform to the National Standard and has high control accuracy. The research includes:a) Study on characteristics of ABS hydraulic control unitThis chapter is the premise of the design of ABS control algorithm. According to the needs of the design, the principle analyses and characteristic study of the ABS hydraulic control unit are carried out. The results will be used to provide theoretical basis for the follow-up research such as the determination of duty cycle of valve drive signal.b) Overall design of ABS control algorithmAfter reading the involved literatures home and abroad, the developing actuality and research hotspots are summed up, and an over-all strategy of ABS control is designed;c) Design of ABS control algorithm based on slip ratioThis chapter is the core of the whole research. It includes: 1). Target slip ratio optimization algorithm. The main feature of the algorithm is that comparative accurate target slip ratio can be calculated only using the value of vehicle deceleration without the road identification; 2). Fuzzy variable structure controller used to calculate target brake torque. In this controller, fuzzy controller is used to real-time regulate the parameters of exponential approach law of the variable structure controller in order to weaken the buffeting of system; 3).Determination of duty cycle of valve drive signal. In this part, the theory of binary discrete function interpolation is applied.d) Simulation verificationIn order to verify the effectiveness and stability of control system, off-line simulation is carried out. For further verification, automobile chassis hardware-in-the-loop test bench based on Matlab/xPC Target and RTW real-time toolbox is built.Of the above research, the main conclusions include:a) Utkin sliding self-optimization theory have showed a good performance in the calculation of target slip ratio, and the accuracy of optimation is improved by introducing a nonlinear link;b) Fuzzy variable structure control can improve the quality of movement to the switching surface and markedly decrease the system buffeting, so that the requires of system real-time and stability is met;c) The method of binary discrete function interpolation can effectively determine the value of duty cycle on a particular pressure difference and pressure change rate with less calculation.