Simulation And Experiment Of Automobile ABS Heat Transfer And Its Brake Force

Along with the development of economy and society progress,automobiles become more and more popular,but problems such as transportation safety,energy consumption,and environmental pollution also arise.Transportation safety has become a worldwide focus,and many automobile passive and active safety devices appear.Anti-lock Braking System(ABS)has been a standard configuration as a significant active safety device,ABS can adjust brake pressure automatically,change the braking torque,shorten braking length,and enhance control ability and directional stability of automobile.Present researches about ABS are focused on control algorithm,pressure regulation,braking system structure and so on.However,the heat transfer and brake force characteristics of ABS has a great influence on automobile brake performance.Heat,environment temperature,water absorption of brake fluid and air have a great impact on brake performance,and there are few researches on the heat transfer and brake force of ABS.Therefore,this thesis presents the heat transfer and brake force characteristics of ABS,and puts forward a method to identify the gas-liquid two-phase flow pattern,Hilbert Huang Transform(HHT)was applied to analyse differential pressure signals,and get energy ratio feature characteristics,and then identify flow pattern based on existing identification criterions of flow pattern,this method can be applied on gas-liquid two-phase flow pattern identification of ABS.This thesis is mainly involving the following tasks:(1)The influences on flow characteristics,brake performance and brake parts which are caused by factors such as heat,environment temperature,water absorption of brake fluid and air are systematically analyzed,the effects of heat transfer are briefly introduced,and finally summarize the research status.(2)Establish a 3-D model of a brake disc by FEMAP,and simulate the heat transfer characteristics of different brake operating conditions.When velocity is 120km/h,the maximum temperature reaches 286.9? after 3.36s;When velocity is 100km/h,the maximum temperature reaches 224.3 ?after 2.8s;When velocity is 60km/h,the maximum temperature reaches 100.9?after 1.84s.The simulation results of brake disc and brake pad on different thickness surface show that:the surface temperature at 6.25mm far from brake disc is 194? while temperature of brake pad is the same as environmental temperature,so friction heat has a greater impact on brake disc than that on brake pad,it is because brake disc has a higher thermal conductivity.Simulation results of continuous brake operating condition when velocity is 60km/h show that temperature is much higher than that of emergency brake operating condition,and the maximum temperature is 376?,the temperature of brake disc surface at 6.25mm far from the frictional surface is evenly distributed while the temperature of brake pad surface at 12mm far from the frictional surface is 130?,it is because heat conduction is sufficient with longer braking time.The simulation results show that heat has a great impact on the brake parts,and heat is a significant factor of gas-liquid two-phase flow.(3)AMESim software is used to study the gas-liquid two-phase flow of ABS.The brake progress will produce a lot of heat and it result in temperature rise of brake system,heat is also a significant influence factor of gas-liquid two-phase flow of ABS,so change the temperature and void fraction during simulation.It takes 3.2s to reach the peak pressure 290kPa when the temperature of brake fluid is 40 ?,the pressure regulating range is 150-290kPa;The time is 4.2s and 6.2s when temperature of brake fluid is 180? and 250 ? respectively,the peak pressure is 280kPa and 260kPa respectively,and the pressure regulating range is 170-280kPa and 180-260kPa respectively.It takes 1.2s,2.2s and3.5s to reach the peak pressure when void fraction is 1%,3%and 5%,the peak pressure is 300kPa,290kPa and 270kPa,the pressure regulating range is 100-300kPa,130-290kPa and 150-270kPa respectively.So when there is gas-liquid two-phase flow,the dynamic response of brake pressure turns to be slow,and pressure regulating range becomes narrow,this will lead to the decreasement of braking torque and accelerated speed,so braking distance extended,and this will have a significant impact on the braking performance.(4)A testbed was designed based on Santana 3000 ABS and experiments were conducted.Dispose pressure data and get differential pressure signal,then utilize HHT to get denoising differential pressure signal,imf and marginal spectrum,when velocity is 30km/h,the signal amplitude is 0-0.2;when velocity is 40km/h,the signal amplitude is 0-0.3;when velocity is 50km/h,the signal amplitude is 0-0.4;so the signal amplitude increases as the initial velocity becomes fast,and it is mainly concentrated in the region of 0-50Hz.Work out the energy ratio of imf and different frequency area,and energy ratio of high frequency area plays a leading role.Flow regime of ABS brake line is bubble flow.Analysis results of temperature show that:temperature is much higher under continuous brake operating condition,temperature rises faster when the initial velocity is quicker and the maximum temperature is much higher,these experimental results is as the same as simulation results.