Investigation On Turbocharger Housing And Bracket Fatigue Failure Problem

In order to cope with the challenges of energy conservation and emission reduction regulations and the increasing performance demand for consumer in recent years,turbocharger technology has been widely used in the global automotive market.In the past five years,engine OEMs in China have gradually transitioned to turbocharged engine development.During the development of a turbocharged engine,the turbocharged housing and its bracket in the hot end of the exhaust system are prone to cracking problems.The uncertainty caused by the design verification through the endurance test during the engine development process,the extension of the test cycle and the additional cost pose risks to the company product development.Therefore,it is important to establish a method for predicting the fatigue performance of the TC housing and the bracket at the initial stage of product design to reduce the risk of product development.In this paper,the TC housing and the bracket are taken as the research object.The fatigue failure is studied by establishing the thermal state numerical simulation method of the TC housing and the bracket.The influencing factors of different working conditions,different structures and different vibration levels are analyzed.According to this,a reasonable optimization scheme is proposed for the cracked TC housing and the bracket,and the scheme is verified and optimized by actual experiment.At the same time,the formed method is applied to other models,which is further verified.The main research contents and conclusions are as followed.1.The numerical simulation model and calculation method of the thermal state of the TC housing and its bracket are established and verified.The analysis results show that the fatigue failure area of the TC housing and the bracket are thermal strain concentrated and bigger than other areas,indicating that the thermal state analysis model and method are accurate,which can provide the basis for the study of subsequent influencing factors.Similarly,this method can be applied to the research and development of fatigue failure of other turbocharged engine TC housing and its bracket.2.The research on the three factors influencing the TC housing fatigue,which are the ultimate temperature,the local structure of the TC housing and the vibration level,is conducted.The influence is also obtained.(1)The maximum equivalent plastic strain at the neck of the TC housing is 6.6% under normal engine operating conditions,and when the exhaust temperature exceeds the limit operating temperature,the equivalent plastic strain becomes 8.6%,which is about 33% higher than the former.(2)Unevenness of the stiffness at the bottom of the bolt lap,resulting in obvious thermal stress and strain concentration,and its equivalent plastic strain has exceeded 2%;the stiffness around another bolt lap is uniform,so that there is no thermal stress strain concentration,and its equivalent plastic strain is 0%.(3)The vibration load has almost no effect on the fatigue characteristics of the TC housing.3.The three influencing factors,which are thermal load,local structure of the bracket and vibration size affecting the fatigue characteristics of the bracket are studied and analyzed,and the influence is obtained.(1)Compared with the cold state,the hot state only causes the modal frequency of the turbocharger and the bracket to reduce by about 30 Hz,which has slight effect on the vibration mode;the stress caused by high temperature on the bracket is greater than by the vibration load,and the fatigue characteristics are also affected.The corresponding is bigger.(2)With the increase of the fillet radius at the transition fillet,the equivalent plastic strain decreases from 0.82% to 0.56% until 0%,and accordingly the fatigue performance is gradually improved.(3)The stress of the supercharger bracket is affected by the vibration load,and the maximum can be up to 100 MPa.As the vibration acceleration increases from 5g to 15 g,and to 25 g,the influence on the bracket stress is also from 10 MPa to 50 MPa,and to 100 MPa.4.The structural optimization scheme for the fatigue failure of TC housing and the bracket is proposed and verified,and the method is extended to the design and development and optimization of other models.