| The brake system is an important part of the automobile,but also an important guarantee for driving safety.The environment in which the brake system operates is complex and variable,and noise may be generated when the operation is unstable.Brake noise not only makes the occupants feel uncomfortable,but also affects the surrounding crowd and the environment.At present,in the field of brake noise calculation and analysis,the influence of braking temperature on noise prediction is rarely considered.However,during the braking process,the braking temperature is high and variable,which has a certain impact on the material characteristics and structural mechanical performance of each part of the brake system.The variable braking environment increases the uncertainty of the braking noise.Therefore,it is necessary to study the time-varying characteristics of the braking noise under the influence of temperature,and find out the influencing factors of the braking instability,which has certain guiding significance for improving braking sound quality.The subject takes an automobile drum brake as the analysis object,and uses the combination of finite element and test to explore its braking noise,and analyzes the unstable time-varying characteristics of the braking under the influence of temperature.Firstly,the three-dimensional digital model is simplified according to the internal structure and braking principle of the drum brake.The finite element model with reasonable structure is established.The free modal calculation analysis and experimental analysis are carried out for each component,The accuracy of the finite element model is verified.Secondly,the thermal-mechanical coupling model of the drum brake is established,then the paper analyzes the structure temperature field and stress field distribution under mechanical and thermal-mechanical coupling conditions.It is found that the brake drum affects the overall structural stress distribution of the brake drum when it rotates,and the contact pressure of the friction lining presents a large distribution at both ends and a small distribution in the middle.The friction heat generating brake drum stress is several times larger than that under pure mechanical conditions.The self-energizing force of the collar shoe and the self-reducing force of the slave shoe cause the contact pressure of the collar and the slave shoe to be asymmetric.Under the deceleration condition,the temperature and stress of the brake drum increase rapidly at first and then decrease slowly.The temperatureand stress of the brake drum are always increased under the dragged condition,and the maximum temperature and maximum stress are at the end of braking.Then the four degree of freedom contact vibration model of drum brake is constructed,and the friction brake noise finite element model is established.The complex eigenvalue analysis method showed that the unstable modal frequencies were mainly concentrated in12 frequency ranges of 3080 Hz,3600Hz,5000 Hz,6560Hz,10500 Hz,11000Hz,11200 Hz,11700Hz,12100 Hz,13100Hz,13600 Hz and 14600 Hz.The noise occurrence frequency measured by the brake bench test is in good agreement with the unstable modal frequency of the numerical analysis,and the noise occurrence degree corresponds to the real part numerical level,which verifies the accuracy of the brake noise finite element model.Temperature is introduced into the braking noise model,and the time-varying characteristics of the elastic modulus,thermal expansion coefficient and the two are combined by the complex eigenvalue method.It is concluded that the effect of elastic modulus on the prediction of braking noise time is nonlinear but not sensitive,and the thermal expansion coefficient has a significant nonlinear effect on braking noise prediction and plays a leading role.The temperature affects the unstable modal frequency,the real part value and the instability tendency through the thermal expansion coefficient,and the introduction of temperature improves the accuracy of the brake noise prediction. |
PDF Full Text Request