Analysis Of Vehicle Stability Influenced By Skid Resistance Of Asphalt Pavement

Traffic safety has always been a common problem all over the world.Investigations of road traffic accidents show most of the traffic accidents on rainy days are related to the decline of skid resistance of pavement surface.As anti-skid performance is worse on wet pavement than dry pavement,driving stability of vehicle declines,and vehicle could possibly encounter hydroplaning when brakes.In this case,traffic accidents are more likely to occur.In order to guarantee vehicle safety,pavements are needed to provide decent skid resistance on rainy days.Research results have certain instruction effect on designing automatic braking system in future automatic drive.Rubber-pavement friction mechanism was analyzed theoretically.Based on Persson friction theory,the power spectrum densities of AC(asphalt concrete),SMA(stone mastic asphalt)and OGFC(open graded friction course)were calculated in MATLAB.Considering the friction mechanism on wet surface with low velocity,friction coefficients between tire rubber and three kind of asphalt pavements in dry and wet conditions were calculated in MATHEMATICA.Then,finite element model of three-dimensional-inflated-patterned tire hydroplaning was built.The friction characteristics was analyzed in tire theory,and friction characteristics curves between asphalt pavement and tire in dry and wet conditions were obtained.Using CoupledEuler-Lagrange method,the process of tire hydroplaning was simulated and verified.The impacts of water film thickness and tire motion status to tire partial hydroplaning performance were examined,and the relation between hydrodynamic force and water film thickness was fitted.Based on these,vehicle dynamic model was built in CarSim,and MATLAB/Simulink was coupled to simulate hydrodynamic force on vehicle tire,to realize the simulation of vehicle driving process on wet pavement.The ABS(antilocked braking system)was analyzed,and vehicle braking distance and lateral offset distance were chosen as indicators to evaluate vehicle driving stability.Choosing different rain intensity,considering water film thickness prediction,vehicle stabilities on different asphalt pavement were compared and analyzed.The methodology of evaluating vehicle stability in dry and wet conditions was founded.The results shows pavement skid resistance is related to power spectrum density of pavement and complex modulus of rubber at the same time.Higher fractal dimension,larger maximum aggregate,and smaller minimum grain,can cause larger calculated kinetic friction coefficient.In wet and low-speed conditions,“the sealing effect” of water film inhibits the contact between rubber and pavement,and the power spectrum density changes.This cause the decline of friction coefficient.In high-speed condition,thicker water film and higher velocity will cause larger hydrodynamic force to tire.Lower vehicle velocity,thinner water film,and ABS can decrease vehicle braking distance effectively.Compared to dry condition,kinetic friction coefficients between rubber and pavement decline about 13%~34%.For dry pavement,the effect of asphalt pavement types to vehicle driving stability could be neglected.For wet pavement,the vehicle stabilities on different pavements fall in sequence of OGFC,SMA and AC.However,when vehicles speed and rain intensity increase,SMA pavement is more dangerous than AC because of thicker water film.Compared with critical tire hydroplaning speed,full vehicle model is superior in coinciding with the actual situation in evaluating vehicle driving performance on wet pavement.Thus braking system need to be analyzed according to vehicle-pavement interaction characteristics in autonomous vehicle,to guarantee driving stability of automatic drive.