Research On Thermal Depression Of Hydraulic Brake System For Small Or Medium Passenger Vehicles

Since the beginning of the new century,with the rapid growth of China's economic stock,the number of vehicles has been increasing at a rapid rate.The annual increase in car ownership reflects the increase in urbanization in China.However,after the rapid increase in the number of cars,it also brought huge security risks to urban road traffic.Hydraulic disc brake is the functional component with the highest operating rate to protect the safety of the driver and passengers.When the car brakes,the kinetic energy of the vehicle is transferred to friction energy and dissipated into the air by the braking system.According to the structure,vehicle brakes can be divided into drum brakes and disc brakes.The former has better heat dissipation performance and anti-water decay performance,and thus is more and more widely used in various types of vehicles.If the temperature of the friction surface for the hydraulic disc brakes of passenger vehicles does not reach the thermal decomposition temperature of the resin friction material,the friction at this time is dry friction.The friction coefficient of the friction surface will slightly increase and then remain unchanged.If the temperature is too high,the friction material of the resin is decomposed by heat,and the friction at this time is mixed friction,which shows the characteristics of abrasive wear and fluid lubrication.The friction factor is significantly reduced.While braking,the braking torque that can be transmitted is rapidly reduced,that is,a thermal decay phenomenon occurs.The disc brakes for vehicles are the functional components with the highest operating rates of the drivers.Directly related to the safety and comfort of the vehicle when vehicle is running normally.While the vehicle is braking,the kinetic energy of the vehicle is dissipated into the air through the frictional process of the braking system.According to the structure,vehicle brakes can be classified into drum brakes and disc brakes.The former has better heat dissipation performance and water repellency,and thus it is more and more widely used in various types of vehicles.In this thesis,the temperature field and braking coefficient of front wheel hydraulically ventilated disc brakes of a passenger vehicle is studied by theoreticalanalysis and numerical simulation.A thermo-mechanical coupling model of the brake is constructed based on ABAQUS finite element analysis software in consideration of convective heat transfer coefficient variation with vehicle speed.The temperature change of the brake is calculated and analyzed under a cyclic braking condition.The change of braking coefficient with temperature is studied according to the test results in the existing literature.It is fitted for the relationship between the braking coefficient and the temperature field of the brake disc.A brief analysis of the factors that affect the brake coefficient of disc brakes is conducted to avoid the phenomenon that the friction coefficient of the brake is reduced due to the high temperature.The brakes of different heat-dissipating fins showed a brief increase in the friction factor at the start of braking,but the growth rate was limited.With the increase in the times of brakes,the friction factor has shown a decline or even a sharp decline in the trend.For brake discs with more fins,the friction factor reduces,and the minimum friction factor can be reduced to 0.233.By analyzing the cyclic braking conditions,when the number of radiating fins is 90,the temperature on the surface of the brake disc is the lowest,and the friction factor decreases slowly.In the conceptual design phase of the brake disc structure,it is advisable to select the brake disc with a large number of radiating fins as much as possible.Finally,the thermal decay of the brake discs is reduced and thereby the reliability of the brake system is increased.