Autonomous Vehicle Safety Brake Simulation Study

This thesis researches on the problem of safe braking of Autonomous Land Vehicle, including theory analysis, mathematical model and simulation of the braking system.At first the whole braking system is divided into three subsystems, brake pedal-brakepipe pressure subsystem, brake pipe pressure-wheel detent subsystem and wheel detent——road subsystem. Their math models are analyzed and developed respectively. The model ofthe brake pedal-brake pipe pressure subsystem is developed by system identificationaccording to the test data of some vehicle. The result of simulation proves that this model reflects the phenomena and characteristic of the subsystem in time delay and glutinosity. The output of sine input and step input is also up to reality.In this thesis the longitudinal force of a moving car is analyzed and a single wheel dynamics model in condition of braking is also developed. According to the shape of thewheel slip (λ) - adhesion coefficient (μ) curve, a method is developed to count thepositive or negative of dμ/dλ by brake moment, velocity and acceleration. Then the wheel slip and the adhesion coefficient between road and wheel can be judged according to dμ/dλ. And a slide mode control is designed to control the brake moment in this thesis so that the vehicle can track the optimal wheel slip. The effectiveness of this method is verified by the result of simulation.The dynamics model of two-wheel vehicle downgrade and braking, along with that of four-wheel vehicle turning and braking is developed in this thesis. The influence of the condition that the parameter of vehicle and road is changed on the braking ability of front-rear wheel and whole vehicle is studied with the two-wheel vehicle model. Some typical brake conditions are simulated with four-wheel vehicle model, such as braking with a lesser brake moment, braking in the optimal slip and braking when wheels are locked. The results of the simulation prove that the vehicle can turning well and the braking distance is shortest when ALV braking in the optimal slip, and it is a perfect braking method. And the condition that rear wheel locked braking should be avoided.