Study On Braking Behavior Of Typical Vehicle Under Moist Or Water Asphalt Pavement Condition

In the rainy day, cars are more prone to traffic accidents. On the one hand, decreased visibility has bad influence on the driver line of sight; on the other hand, the rainwater flow on the road and form a layer of water film. The adhesion coefficient between tire and road surface decreases significantly. Therefore, the study plays an important role to improve the road traffic safety.Firstly, the author analysis the stress and motion state of the wheel from the mechanics and dynamics points of view. By analyzing the relationship between ground braking force, braking force and adhesion, facts show that the ground braking force is proportional to the braking force. But the maximum value of ground braking force is not more than adhesion. By analyzing the relationship between slip ratio and adhesion coefficient, facts show that the maximum value of adhesion coefficient occurs when the tire remains optimal slip ratio.According to the elasto-hydrodynamic lubrication theory, the performance of dynamic hydroplaning of tire is analyzed and the hydroplaning critical velocity model is built. According to the multiple linear regression theory, the model of the relationship between speeds, water film thickness and tire tread depth is built. Classify pavement condition by water film thickness, and identify the adhesion coefficient model of different pavement condition.The Dynamic adhesion coefficient was defined with the discrete method of loop iterations by using CarSim software. Simulation results show that braking distance increases with the increase of water film thickness and speed; braking distance decreases with the increase of tire tread depth. Speed has the most important influence in braking distance. Therefore, reducing the speed is the most effective way to keep safty and avoid traffic accident.Finally, considering the driver’s reaction characteristics during braking, the safe driving distance model was set up by using automotive brake simulation results. The safe driving distance of double car model system was determined by analyzing the different motion state of previous vehicles. The safe driving speed and distance under different rainfall intensity were calculated based on the safe driving distance model, then some suggestions was put forward for highway safety driving on rainy days.