Failure Analysis And Optimal Design Of Valve Train In 1.0L Turbocharged Diesel Engine

The valve train mechanism,one of the important engine components,is used for gas exchanging.The system has many failure problems because of the severe working conditions.Therefore,it needs to conduct the failure analysis and optimal design for this system.The 1.0L turbocharged diesel engine made by Chery Automobile Company had a torque fluctuation problem because of the wear failure occurred in the valve train system.The wear failures are caused by the friction between exhaust valve stem end and roller finger follower pallet,the friction between valve stem and valve guide,and the friction between valve and seat.This thesis focuses on this valve train,and investigates the wear failure reason to find a solution to solve the problems finally.The wear problems of the three parts are all related to the layout design of the valve train mechanism.This paper systematically analyzes and summarizes the three wear problems.It is found that there is an unreasonable design in the arrangement of the rocker tappet,the end of the valve rod,the valve and the arrangement of the conduit,and it is easy to form a larger lateral force.Through the kinematic analysis of the valve train mechanism,the formula of the slip distance and the slip velocity of the contact point of the valve rod end and the rocker arm is derived,and the factors affecting the force of the valve tube are analyzed.The dynamic simulation of valve train is carried out,and the valve seat speed and seat force are analyzed.Through calculation and simulation,it is found that the eccentric distance of the contact point of the valve rod end of the valve mechanism is large and the slip velocity is too large,which leads to the excessive lateral force of the valve and the conduit,so that the valve rod end,valve tube and valve seat have the risk of wear from top to bottom.At the same time,the tribology and wear mechanism were preliminarily analyzed,and three wear problems were compared.On the basis of theoretical and simulation analysis,the optimization design scheme is put forward respectively: 1)In the aspect of valve end wear,three optimization schemes are put forward in the layout of tappet.After comparing and calculating the slip velocity and contact stress,the optimal scheme is to determine the tappet moving down 2.5mm and moving 0.5mm.2)In wear and tear of the valve tube,the placement of the pipe,and the cylinder liner are optimized to reduce the temperature of the exhaust pipe by 132.7 degrees.3)In wear of the valve seat,the cylinder head water jacket around the exhaust seat is optimized to reduce the temperature of the seat ring by 34 degrees Celsius,and reduce the valve temperature by 40 degrees Celsius.Through the above optimization measures,the stress of each part is reduced,the amplitude of high temperature hardness and the wear are reduced as well.Through the dynamic test of the valve train mechanism,the optimization design and the original scheme are compared and verified.It is found that the force of the rocker arm and the speed of the valve seat are all improved obviously.Through the comparison of the durability test of the ignition bench,the three friction pairs of the optimized friction pairs decreased significantly,and the torque ripple in the earlier stage was not reproduced in the optimized test.The research work of this paper solves the problem of wear and tear failure of the valve train mechanism of the company,and lays a good foundation for the technical upgrading of the diesel engine and the optimization design of the valve train mechanism in the future.