Fault Analysis And Improvement Of The Rocker Arm Fracture Of A Diesel Engine

The research content of this paper belongs to the category of the horizontal subject,a certain type of diesel engine has trouble with the valve train,the main failure phenomenon: the rocker arm fracture、push rod bended、timing belt jump teeth about 2.5 teeth、there also has camshaft、camshaft bearing、cam lift section and tappet section have wear phenomena,other phenomena such as the top of the piston is normal,no obvious impact valve.The starting point of this study is to use the rocker arm as the starting point,and the mechanical structure of the exhaust valve rocker arm is analyzed in detail,and the fault analysis of valve is analyzed in detail,the research substance and summings-up of the paper are as follows:1、 Firstly,the influence of all possible factors on the failure of the valve train is analyzed,draw the diagram of the fault factors,there is a sudden impact of cold start、the movement interference of the valve parts、poor engine parts dimension、engine lubrication system failure、engine cleanliness、cleanliness of parts and components and poor heat treatment of parts,and at the end of the article to do a detailed explanation.2、 The exhaust valve rocker arm and exhaust valve of the mechanical structure analysis,which obtain the rocker arm ratio is 1.426,when the engine is burning,the force required to open the exhaust valve is 1585 N,this provides data support for the simulation calculation of the rocker arm.The positioning slot structure of rocker arm push rod end is analyzed,and results the movement interference of the valve train is eliminated due to the factors of putting out of the positioning slot.3、 The impact of the rocker arm at room temperature and cold conditions of the impact test has been analyzed,and the conclusion is: the impact times of the rocker arm under normal temperature are greater than the number of the fracture impact under the cold condition,and there is slight difference in the performance of different manufacturers.4、 The rocker arm can be obtained by simulation analysis,and the conclusion: under the engine normal combustion condition,the maximum stress intensity of the rocker arm is 51.85 MPa,far less than the 7075 Aluminum Alloy material yield strength limit 505 MPa,the strength index of the rocker arm meets the design requirements.In the calculation of the maximum yield strength of the rocker arm,it is concluded that the burst pressure of the cylinder is 12.20 MPa,which is much higher than that of the cylinder during the normal combustion of the engine,so it can be ruled out simply because of the cold start of the impact factors caused by the rocker arm fracture.The maximum stress of the rocker arm is near the adjusting screw oil hole position,can offer support for the improvement of the rocker arm.By analyzing the frequency value of each modal frequency of the rocker arm,it is not in the frequency range of the normal operation of the engine.5、 The optimal design of the rocker arm is carried out by the finite element topology optimization technique,after improving the rocker arm oil hole,the maximum stress point is not in the oil hole.After eliminating the influence of the rocker itself on the failure of the valve train,and detailed analysis of all possible factors on the impact of the fault.And communicate with the Engineer,The most likely cause of the failure of this type of gas distribution mechanism is the instability of the lubrication system and the tolerance of parts,thus forming a vicious cycle,resulting in a series of fault phenomena.