| Disc braking is the basic braking method for high-speed trains.The most effective method for testing disc braking performance is the 1:1 bench test.However,factors such as expensive equipment and high test cost aggravate research and development costs.The reduced test is a test method for reducing the ratio based on the actual braking conditions.It has the advantages of low cost and short test time.However,there is a deviation between the reduced test and the 1:1 test.Therefore,studying the deviation of the two test methods in terms of friction pair temperature,friction coefficient and the factors that affect the deviation will help to use the reduced test to detect the disc braking performance.In this paper,a comparative braking test was carried out using a reduced test bench and a 1:1 vehicle brake test bench at the speed of 50～220km/h and the pressure of 0.19～0.49 MPa.Using ADINA finite element software,the disc temperature,braking time of the two test methods are calculated.On this basis,the design of the reduced friction pair is carried out,and the effects of the friction arc length,reduced ratio,the temperature field distribution of the 1:1 and reduced disc surface and the braking time are analyzed.The conclusions are as follows:(1)In the numerical simulation,it is found that the peak temperature of the reduced disc is higher than the peak temperature of the 1:1 disc surface.After exceeding the peak temperature,the temperature difference occurs,and the difference increases with the increase of braking pressure.The reason is that with the braking pressure increasing,the braking time decreases.The smaller braking time is equivalent to increasing the braking power and reducing the heat dissipation time,while the concentration of the friction arc distribution increases the concentration of heat,thus results in that after the time of peak temperature the reduced peak temperature is significantly higher than the temperature of 1:1 under the high braking pressure.(2)The braking test shows that the peak temperature of the reduced disc surface is higher than 1:1 test,and the peak temperature difference slightly decreases with the increase of braking pressure.The braking pressure is 0.19 MPa,the initial braking speed is increased from 120km/h to 220km/h,the difference in the peak surface temperature is increased from 40℃ to 88℃,and when the braking pressure is 0.49 MPa,the temperature difference value is between 33 ～ 53℃.The temperature difference caused by the two test methods is difference in cooling conditions and the distribution of friction arc length,making the temperature uniformity of the disc surface better than the reduced test.(3)The braking pressure changes the temperature of the disc surface and affects the friction coefficient of the 1:1 and reduced test methods.At low braking pressure,the peak temperature is less than 400℃,the mechanical properties of the friction material are good,and the proportion of the actual contact area of the brake pad of reduced test is large,so the friction coefficient is higher than the 1:1 condition.At high braking pressures,the excessively high disc surface temperature softens the brake pad material,exacerbating the attenuation of the friction coefficient under reduced test conditions,resulting in the friction coefficient less than that of 1:1 friction pair.(4)The design and simulation calculation of the reduced friction pair indicate that the deviation of the reduced from the 1:1 braking performance lies in the distribution form of the disc surface heat.The temperature distribution is similar to the cooling rate of the disc surface and the braking time. |
PDF Full Text Request