| As one kind of active driver assistance systems, Anti-lock Braking System plays an important part in maintaining vehicle stability and shortening brake distance. Almost all new cars are offered today with ABS. To some extend, this technology has come to perfection abroad, while the domestic research is only in its infancy. The core technology of ABS involves developments of ECU, control strategies, HCU, sensors, and evaluations for brake system-matching. As the actuator of the system, HCU directly affects the performance.ABS is used to control the force applied on the tires in an effort to optimize vehicle performance. Because the force applied on the tires is so critical to ABS, it obviously would be an advantage to know the force directly. Unfortunately, there is currently not an easy and cost-effective way to measure the force. As a secondary solution, the brake pressure could be achieved using pressure sensors whose measurements are can be used by ABS strategy; however, this approach also involves an increase in manufacturing cost of the device. The brake pressure can be estimated by the characteristics of the hydraulic modulator, which is used to perform the ABS brake pressure regulation. This paper presents a brake pressure estimation algorithm for anti-lock braking system which gives accurate and real-time pressure estimation. This paper is carried out as follows:Above all, theoretical analysis to the hydraulic control unit is carried out. The performances of high speed digital valves, including operating feature, dynamic performance and static performance, are studied firstly. On the basis of theoretical analysis to high speed digital valves, the model of hydraulic control unit for ABS is developed using AMESim. Through the simulation, several results are achieved, including the varieties of pressure, flow rate and volume of wheel cylinder. So are the variety of characteristic parameters of the accumulator, the pump, especially control valves. These results reflect dynamic characteristics of the system well.Secondly, based on the data accumulated a reduced mathematics model of the Anti-lock Braking System is developed, which consists of a brake pedal, a master cylinder, a vacuum booster, a hydraulic control unit, lines and brakes, etc. This model explicitly describes the nonlinear capacitance of the brake system. Furthermore, the model allows for brake pressure variations between wheels. The final aspect of the model, therefore, involves relating the wheel pressure to the displaced fluid volume. Finally, a concept of the hydraulic model and inversed hydraulic model is presented, which is the theoretical principle of brake pressure estimating and controlling.Thirdly, two methods of estimating the brake pressure is present on the principle of hydraulic drive and the characteristics of ABS in this paper. One approach relies on the empirical model. This kind of estimation algorithm derived from numerous of vehicle tests to determine the functions of brake pressure under kinds of work condition, which is not available under current stage. Another approach is to develop a model-based brake pressure estimation strategy. The model-based brake pressure estimation strategy is developed in terms of relating the wheel pressure to the displaced fluid volume.Finally, simulated studies of an anti-lock braking system are undertaken using Matlab/Simulink. The simulation is carried out step by step. The model of the anti-lock braking system is built to estimate the brake pressure and a simulation is performed. Then the modulation of the pressure is simulated using Stateflow. The simulation results show that the algorithm gives accurate pressure estimation.
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